MCAT Practice Questions (2026) — Free Sample Questions with Answers

Separating and Quantifying a Three-Component Mixture

¹Acid–base extraction separates organic compounds by converting some of them into water-soluble ions. A student was given 1.00 g of a mixture of benzoic acid ($\text{p}{K}_a$ 4.2), 2-naphthol ($\text{p}{K}_a$ 9.5), and naphthalene, a hydrocarbon with no acidic proton, and was asked to separate the three components and identify each by spectroscopy. The $\text{p}{K}_a$ of carbonic acid, the conjugate acid of bicarbonate, is 6.4.

²The mixture was dissolved in diethyl ether and extracted twice with saturated aqueous NaHCO${}_3$, with the separatory funnel vented after each shaking. The aqueous layer was acidified with HCl, and the solid that precipitated was collected as fraction 1. The ether layer was then extracted with 1 M NaOH, and this aqueous layer was acidified in the same way to give fraction 2. The remaining ether layer was dried and evaporated to give fraction 3. Each fraction was analyzed by IR spectroscopy (Table 1), and its purity was checked by thin-layer chromatography (TLC) on silica gel.

³To estimate how much 2-naphthol was recovered, the student dissolved all of fraction 2 in ethanol to a total volume of 100 mL. A sample of this solution was diluted 10-fold with ethanol, and its absorbance at 330 nm in a 1.0 cm cuvette was 0.40. The student applied the Beer–Lambert law, $A=\epsilon bc$, using a molar absorptivity for 2-naphthol at this wavelength of $2.0\times 10^3$ M${}^{-1}$cm${}^{-1}$, determined from standard solutions. The dried mass of fraction 2 was also recorded so that the two estimates of recovery could be compared.

Separating and Quantifying a Three-Component Mixture

¹Acid–base extraction separates organic compounds by converting some of them into water-soluble ions. A student was given 1.00 g of a mixture of benzoic acid ($\text{p}{K}_a$ 4.2), 2-naphthol ($\text{p}{K}_a$ 9.5), and naphthalene, a hydrocarbon with no acidic proton, and was asked to separate the three components and identify each by spectroscopy. The $\text{p}{K}_a$ of carbonic acid, the conjugate acid of bicarbonate, is 6.4.

²The mixture was dissolved in diethyl ether and extracted twice with saturated aqueous NaHCO${}_3$, with the separatory funnel vented after each shaking. The aqueous layer was acidified with HCl, and the solid that precipitated was collected as fraction 1. The ether layer was then extracted with 1 M NaOH, and this aqueous layer was acidified in the same way to give fraction 2. The remaining ether layer was dried and evaporated to give fraction 3. Each fraction was analyzed by IR spectroscopy (Table 1), and its purity was checked by thin-layer chromatography (TLC) on silica gel.

³To estimate how much 2-naphthol was recovered, the student dissolved all of fraction 2 in ethanol to a total volume of 100 mL. A sample of this solution was diluted 10-fold with ethanol, and its absorbance at 330 nm in a 1.0 cm cuvette was 0.40. The student applied the Beer–Lambert law, $A=\epsilon bc$, using a molar absorptivity for 2-naphthol at this wavelength of $2.0\times 10^3$ M${}^{-1}$cm${}^{-1}$, determined from standard solutions. The dried mass of fraction 2 was also recorded so that the two estimates of recovery could be compared.

Separating and Quantifying a Three-Component Mixture

¹Acid–base extraction separates organic compounds by converting some of them into water-soluble ions. A student was given 1.00 g of a mixture of benzoic acid ($\text{p}{K}_a$ 4.2), 2-naphthol ($\text{p}{K}_a$ 9.5), and naphthalene, a hydrocarbon with no acidic proton, and was asked to separate the three components and identify each by spectroscopy. The $\text{p}{K}_a$ of carbonic acid, the conjugate acid of bicarbonate, is 6.4.

²The mixture was dissolved in diethyl ether and extracted twice with saturated aqueous NaHCO${}_3$, with the separatory funnel vented after each shaking. The aqueous layer was acidified with HCl, and the solid that precipitated was collected as fraction 1. The ether layer was then extracted with 1 M NaOH, and this aqueous layer was acidified in the same way to give fraction 2. The remaining ether layer was dried and evaporated to give fraction 3. Each fraction was analyzed by IR spectroscopy (Table 1), and its purity was checked by thin-layer chromatography (TLC) on silica gel.

³To estimate how much 2-naphthol was recovered, the student dissolved all of fraction 2 in ethanol to a total volume of 100 mL. A sample of this solution was diluted 10-fold with ethanol, and its absorbance at 330 nm in a 1.0 cm cuvette was 0.40. The student applied the Beer–Lambert law, $A=\epsilon bc$, using a molar absorptivity for 2-naphthol at this wavelength of $2.0\times 10^3$ M${}^{-1}$cm${}^{-1}$, determined from standard solutions. The dried mass of fraction 2 was also recorded so that the two estimates of recovery could be compared.

Passage 6

¹Among the tools that public health agencies have embraced in recent decades, few have been greeted as warmly as the "nudge": an alteration in the way choices are presented that steers people toward healthier options without forbidding any alternative. Place fruit at eye level in the cafeteria and the pastries at the back; make organ donation or retirement saving the default and require those who object to opt out. Defenders describe such measures as uniquely respectful of liberty. Nothing is banned, no one is fined, and anyone who wishes to choose otherwise remains free to do so. The appeal to officials is easy to see as well: such measures are cheap, require no new legislation, and spare them the unpopular work of prohibition.

²The argument has force, and it is worth stating why. Every choice is presented in some way; there is no neutral cafeteria in which food is arranged by no one for no purpose. If arrangement is unavoidable, the defenders reason, it may as well be arranged to promote health. Refusing to nudge is not abstaining from influence but merely choosing influence of a different, unexamined kind—whatever pleases the vendor, or whatever happened to be convenient for the staff who stocked the shelves.

³Yet the claim that nudges preserve liberty depends on a picture of freedom that is too thin. On that picture, I am free so long as the alternatives remain formally available—so long as I could, if I wished, reach past the fruit for the pastry. My freedom, so understood, is measured by the menu rather than by my attention to it. But nudges work precisely because people do not, in the ordinary course of things, scrutinize the arrangement of their options. A default succeeds to the degree that it is not noticed. The measure that most reliably changes behavior is therefore the one least likely to engage the deliberation through which people exercise the liberty the defenders invoke.

⁴This does not make nudges illegitimate, but it relocates the question of their legitimacy. The relevant test is not whether an alternative exists but whether the nudge could survive being made public. A cafeteria that posts a sign explaining that fruit is placed at eye level to encourage healthier eating, and a pension plan that tells employees plainly why enrollment is automatic, invite the very scrutiny that the nudge would otherwise bypass. If the measure keeps most of its effect once disclosed, that is some evidence that it works with the considered preferences of those it steers; if it loses most of its effect, that is evidence that it was working against them.

⁵Some defenders will object that disclosure would defeat the purpose—that a nudge announced is a nudge disarmed. The evidence on this point is less settled than either side tends to admit, but the objection, if true, would prove too much. A policy that can achieve its ends only so long as its targets remain unaware of it has more in common with manipulation than with the respectful guidance its champions describe. Public health has every reason to arrange choices thoughtfully. It has no reason to prefer arrangements that cannot bear the light.

Passage 6

¹Among the tools that public health agencies have embraced in recent decades, few have been greeted as warmly as the "nudge": an alteration in the way choices are presented that steers people toward healthier options without forbidding any alternative. Place fruit at eye level in the cafeteria and the pastries at the back; make organ donation or retirement saving the default and require those who object to opt out. Defenders describe such measures as uniquely respectful of liberty. Nothing is banned, no one is fined, and anyone who wishes to choose otherwise remains free to do so. The appeal to officials is easy to see as well: such measures are cheap, require no new legislation, and spare them the unpopular work of prohibition.

²The argument has force, and it is worth stating why. Every choice is presented in some way; there is no neutral cafeteria in which food is arranged by no one for no purpose. If arrangement is unavoidable, the defenders reason, it may as well be arranged to promote health. Refusing to nudge is not abstaining from influence but merely choosing influence of a different, unexamined kind—whatever pleases the vendor, or whatever happened to be convenient for the staff who stocked the shelves.

³Yet the claim that nudges preserve liberty depends on a picture of freedom that is too thin. On that picture, I am free so long as the alternatives remain formally available—so long as I could, if I wished, reach past the fruit for the pastry. My freedom, so understood, is measured by the menu rather than by my attention to it. But nudges work precisely because people do not, in the ordinary course of things, scrutinize the arrangement of their options. A default succeeds to the degree that it is not noticed. The measure that most reliably changes behavior is therefore the one least likely to engage the deliberation through which people exercise the liberty the defenders invoke.

⁴This does not make nudges illegitimate, but it relocates the question of their legitimacy. The relevant test is not whether an alternative exists but whether the nudge could survive being made public. A cafeteria that posts a sign explaining that fruit is placed at eye level to encourage healthier eating, and a pension plan that tells employees plainly why enrollment is automatic, invite the very scrutiny that the nudge would otherwise bypass. If the measure keeps most of its effect once disclosed, that is some evidence that it works with the considered preferences of those it steers; if it loses most of its effect, that is evidence that it was working against them.

⁵Some defenders will object that disclosure would defeat the purpose—that a nudge announced is a nudge disarmed. The evidence on this point is less settled than either side tends to admit, but the objection, if true, would prove too much. A policy that can achieve its ends only so long as its targets remain unaware of it has more in common with manipulation than with the respectful guidance its champions describe. Public health has every reason to arrange choices thoughtfully. It has no reason to prefer arrangements that cannot bear the light.

Passage 6

¹Among the tools that public health agencies have embraced in recent decades, few have been greeted as warmly as the "nudge": an alteration in the way choices are presented that steers people toward healthier options without forbidding any alternative. Place fruit at eye level in the cafeteria and the pastries at the back; make organ donation or retirement saving the default and require those who object to opt out. Defenders describe such measures as uniquely respectful of liberty. Nothing is banned, no one is fined, and anyone who wishes to choose otherwise remains free to do so. The appeal to officials is easy to see as well: such measures are cheap, require no new legislation, and spare them the unpopular work of prohibition.

²The argument has force, and it is worth stating why. Every choice is presented in some way; there is no neutral cafeteria in which food is arranged by no one for no purpose. If arrangement is unavoidable, the defenders reason, it may as well be arranged to promote health. Refusing to nudge is not abstaining from influence but merely choosing influence of a different, unexamined kind—whatever pleases the vendor, or whatever happened to be convenient for the staff who stocked the shelves.

³Yet the claim that nudges preserve liberty depends on a picture of freedom that is too thin. On that picture, I am free so long as the alternatives remain formally available—so long as I could, if I wished, reach past the fruit for the pastry. My freedom, so understood, is measured by the menu rather than by my attention to it. But nudges work precisely because people do not, in the ordinary course of things, scrutinize the arrangement of their options. A default succeeds to the degree that it is not noticed. The measure that most reliably changes behavior is therefore the one least likely to engage the deliberation through which people exercise the liberty the defenders invoke.

⁴This does not make nudges illegitimate, but it relocates the question of their legitimacy. The relevant test is not whether an alternative exists but whether the nudge could survive being made public. A cafeteria that posts a sign explaining that fruit is placed at eye level to encourage healthier eating, and a pension plan that tells employees plainly why enrollment is automatic, invite the very scrutiny that the nudge would otherwise bypass. If the measure keeps most of its effect once disclosed, that is some evidence that it works with the considered preferences of those it steers; if it loses most of its effect, that is evidence that it was working against them.

⁵Some defenders will object that disclosure would defeat the purpose—that a nudge announced is a nudge disarmed. The evidence on this point is less settled than either side tends to admit, but the objection, if true, would prove too much. A policy that can achieve its ends only so long as its targets remain unaware of it has more in common with manipulation than with the respectful guidance its champions describe. Public health has every reason to arrange choices thoughtfully. It has no reason to prefer arrangements that cannot bear the light.

Passage 6

¹Among the tools that public health agencies have embraced in recent decades, few have been greeted as warmly as the "nudge": an alteration in the way choices are presented that steers people toward healthier options without forbidding any alternative. Place fruit at eye level in the cafeteria and the pastries at the back; make organ donation or retirement saving the default and require those who object to opt out. Defenders describe such measures as uniquely respectful of liberty. Nothing is banned, no one is fined, and anyone who wishes to choose otherwise remains free to do so. The appeal to officials is easy to see as well: such measures are cheap, require no new legislation, and spare them the unpopular work of prohibition.

²The argument has force, and it is worth stating why. Every choice is presented in some way; there is no neutral cafeteria in which food is arranged by no one for no purpose. If arrangement is unavoidable, the defenders reason, it may as well be arranged to promote health. Refusing to nudge is not abstaining from influence but merely choosing influence of a different, unexamined kind—whatever pleases the vendor, or whatever happened to be convenient for the staff who stocked the shelves.

³Yet the claim that nudges preserve liberty depends on a picture of freedom that is too thin. On that picture, I am free so long as the alternatives remain formally available—so long as I could, if I wished, reach past the fruit for the pastry. My freedom, so understood, is measured by the menu rather than by my attention to it. But nudges work precisely because people do not, in the ordinary course of things, scrutinize the arrangement of their options. A default succeeds to the degree that it is not noticed. The measure that most reliably changes behavior is therefore the one least likely to engage the deliberation through which people exercise the liberty the defenders invoke.

⁴This does not make nudges illegitimate, but it relocates the question of their legitimacy. The relevant test is not whether an alternative exists but whether the nudge could survive being made public. A cafeteria that posts a sign explaining that fruit is placed at eye level to encourage healthier eating, and a pension plan that tells employees plainly why enrollment is automatic, invite the very scrutiny that the nudge would otherwise bypass. If the measure keeps most of its effect once disclosed, that is some evidence that it works with the considered preferences of those it steers; if it loses most of its effect, that is evidence that it was working against them.

⁵Some defenders will object that disclosure would defeat the purpose—that a nudge announced is a nudge disarmed. The evidence on this point is less settled than either side tends to admit, but the objection, if true, would prove too much. A policy that can achieve its ends only so long as its targets remain unaware of it has more in common with manipulation than with the respectful guidance its champions describe. Public health has every reason to arrange choices thoughtfully. It has no reason to prefer arrangements that cannot bear the light.

A viral protein that halts the host cell cycle

¹Retroviruses carry two copies of a single-stranded RNA genome together with reverse transcriptase and integrase inside the virion. After the virus enters a cell, reverse transcriptase copies the genome into double-stranded DNA, which integrase inserts into a host chromosome as a provirus. Host RNA polymerase II then transcribes viral genes. Some retroviruses also package small accessory proteins in the virion along with the enzymes.

²Researchers studied accessory protein V of a primate retrovirus. Dividing human T cells were mock infected, infected with wild-type virus, or infected with a mutant virus that does not make V (ΔV). A fourth culture received wild-type virus plus a reverse transcriptase inhibitor added 1 h before infection; the inhibitor alone did not change the cell-cycle profile of uninfected cells. After 24 h, cells were stained with a fluorescent DNA-binding dye and analyzed by flow cytometry, which classifies each cell by DNA content as G1 (2n), S (between 2n and 4n) or G2/M (4n) (Table 1). Infection conditions were chosen so that more than 90% of cells in each infected culture received virus.

³Western blotting confirmed that V protein is present in purified virions. In infected cells, V was found bound to a phosphatase that normally removes inhibitory phosphates from the cyclin-dependent kinase that triggers entry into mitosis.

⁴Mutations arise often during retroviral replication because reverse transcriptase lacks proofreading activity. As a result, a single infected culture contains many genetically distinct viral variants, and most new mutations either reduce viral replication or have no detectable effect.

A viral protein that halts the host cell cycle

¹Retroviruses carry two copies of a single-stranded RNA genome together with reverse transcriptase and integrase inside the virion. After the virus enters a cell, reverse transcriptase copies the genome into double-stranded DNA, which integrase inserts into a host chromosome as a provirus. Host RNA polymerase II then transcribes viral genes. Some retroviruses also package small accessory proteins in the virion along with the enzymes.

²Researchers studied accessory protein V of a primate retrovirus. Dividing human T cells were mock infected, infected with wild-type virus, or infected with a mutant virus that does not make V (ΔV). A fourth culture received wild-type virus plus a reverse transcriptase inhibitor added 1 h before infection; the inhibitor alone did not change the cell-cycle profile of uninfected cells. After 24 h, cells were stained with a fluorescent DNA-binding dye and analyzed by flow cytometry, which classifies each cell by DNA content as G1 (2n), S (between 2n and 4n) or G2/M (4n) (Table 1). Infection conditions were chosen so that more than 90% of cells in each infected culture received virus.

³Western blotting confirmed that V protein is present in purified virions. In infected cells, V was found bound to a phosphatase that normally removes inhibitory phosphates from the cyclin-dependent kinase that triggers entry into mitosis.

⁴Mutations arise often during retroviral replication because reverse transcriptase lacks proofreading activity. As a result, a single infected culture contains many genetically distinct viral variants, and most new mutations either reduce viral replication or have no detectable effect.

A viral protein that halts the host cell cycle

¹Retroviruses carry two copies of a single-stranded RNA genome together with reverse transcriptase and integrase inside the virion. After the virus enters a cell, reverse transcriptase copies the genome into double-stranded DNA, which integrase inserts into a host chromosome as a provirus. Host RNA polymerase II then transcribes viral genes. Some retroviruses also package small accessory proteins in the virion along with the enzymes.

²Researchers studied accessory protein V of a primate retrovirus. Dividing human T cells were mock infected, infected with wild-type virus, or infected with a mutant virus that does not make V (ΔV). A fourth culture received wild-type virus plus a reverse transcriptase inhibitor added 1 h before infection; the inhibitor alone did not change the cell-cycle profile of uninfected cells. After 24 h, cells were stained with a fluorescent DNA-binding dye and analyzed by flow cytometry, which classifies each cell by DNA content as G1 (2n), S (between 2n and 4n) or G2/M (4n) (Table 1). Infection conditions were chosen so that more than 90% of cells in each infected culture received virus.

³Western blotting confirmed that V protein is present in purified virions. In infected cells, V was found bound to a phosphatase that normally removes inhibitory phosphates from the cyclin-dependent kinase that triggers entry into mitosis.

⁴Mutations arise often during retroviral replication because reverse transcriptase lacks proofreading activity. As a result, a single infected culture contains many genetically distinct viral variants, and most new mutations either reduce viral replication or have no detectable effect.

Fertility Decline and Schooling in a Lower-Middle-Income Country

¹Demographers studying a lower-middle-income country compiled national registration data from 1900 to 2020 (Table 1) to examine its demographic transition. The crude birth rate (CBR) and crude death rate (CDR) are expressed per 1,000 population per year; the rate of natural increase equals CBR minus CDR. Migration into and out of the country was negligible throughout the period, and the population grew from about 6 million in 1900 to about 40 million in 2020.

²Over the same period, the country expanded public education. Enrollment of girls in secondary school rose from a small minority to nearly all eligible girls, and the average age at first marriage increased. Over the same decades, infant mortality fell sharply, and the labor force shifted from agriculture toward manufacturing and services. By 2020, women completed an average of 11 years of schooling, compared with fewer than 2 years in 1900.

³Two research teams interpreted the fertility decline differently. Team 1 argued that as the economy industrialized, mass schooling met society's need for literate workers, and smaller families followed as children shifted from contributing household labor to requiring years of costly education. In this account, education and the family adjusted to one another in ways that kept society stable. Team 2 argued that expanded schooling for girls was won through decades of struggle by women's organizations against political elites, and that fertility fell as women gained power over household decisions.

⁴Team 1 further concluded from Table 1 that each additional year of schooling a woman received caused her to have fewer children.

Fertility Decline and Schooling in a Lower-Middle-Income Country

¹Demographers studying a lower-middle-income country compiled national registration data from 1900 to 2020 (Table 1) to examine its demographic transition. The crude birth rate (CBR) and crude death rate (CDR) are expressed per 1,000 population per year; the rate of natural increase equals CBR minus CDR. Migration into and out of the country was negligible throughout the period, and the population grew from about 6 million in 1900 to about 40 million in 2020.

²Over the same period, the country expanded public education. Enrollment of girls in secondary school rose from a small minority to nearly all eligible girls, and the average age at first marriage increased. Over the same decades, infant mortality fell sharply, and the labor force shifted from agriculture toward manufacturing and services. By 2020, women completed an average of 11 years of schooling, compared with fewer than 2 years in 1900.

³Two research teams interpreted the fertility decline differently. Team 1 argued that as the economy industrialized, mass schooling met society's need for literate workers, and smaller families followed as children shifted from contributing household labor to requiring years of costly education. In this account, education and the family adjusted to one another in ways that kept society stable. Team 2 argued that expanded schooling for girls was won through decades of struggle by women's organizations against political elites, and that fertility fell as women gained power over household decisions.

⁴Team 1 further concluded from Table 1 that each additional year of schooling a woman received caused her to have fewer children.

Fertility Decline and Schooling in a Lower-Middle-Income Country

¹Demographers studying a lower-middle-income country compiled national registration data from 1900 to 2020 (Table 1) to examine its demographic transition. The crude birth rate (CBR) and crude death rate (CDR) are expressed per 1,000 population per year; the rate of natural increase equals CBR minus CDR. Migration into and out of the country was negligible throughout the period, and the population grew from about 6 million in 1900 to about 40 million in 2020.

²Over the same period, the country expanded public education. Enrollment of girls in secondary school rose from a small minority to nearly all eligible girls, and the average age at first marriage increased. Over the same decades, infant mortality fell sharply, and the labor force shifted from agriculture toward manufacturing and services. By 2020, women completed an average of 11 years of schooling, compared with fewer than 2 years in 1900.

³Two research teams interpreted the fertility decline differently. Team 1 argued that as the economy industrialized, mass schooling met society's need for literate workers, and smaller families followed as children shifted from contributing household labor to requiring years of costly education. In this account, education and the family adjusted to one another in ways that kept society stable. Team 2 argued that expanded schooling for girls was won through decades of struggle by women's organizations against political elites, and that fertility fell as women gained power over household decisions.

⁴Team 1 further concluded from Table 1 that each additional year of schooling a woman received caused her to have fewer children.