MCAT Chemical Physical Foundations
Biological Systems Prep Pack Exam Official
Practice Exam Actual Exam 2026/2027 with
Detailed Rationales | Complete Exam-Style
Questions | Pass Guaranteed – A+ Graded
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SECTION 1: GENERAL CHEMISTRY Q1 – Q13
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Question 1 of 50
A patient with hyperthyroidism receives radioactive iodine-131 therapy. I-131 decays by
emitting a beta particle. If a neutral I-131 atom undergoes this decay, what is the resulting
ion's charge?
A. -1
B. 0
C. +1 ✓ CORRECT
D. +2
Correct Answer: C
Rationale: Beta decay converts a neutron to a proton and an electron; the electron is emitted,
leaving the nucleus with one extra proton and the same electron count, yielding a +1 cation.
Choice A incorrectly assumes the emitted electron remains with the atom. On test day,
remember that beta particles are emitted, not retained.
Question 2 of 50
A researcher is studying the anesthetic gas nitrous oxide (N2O) used in dental procedures. In
the most stable Lewis structure of N2O, what is the approximate bond angle at the central
nitrogen atom?
A. 90°
B. 180° ✓ CORRECT
C. 109.5°
D. 120°
,Correct Answer: B
Rationale: The most stable resonance structure of N2O has a linear geometry with the central
N sp-hybridized, giving a 180° bond angle. Choice C confuses N2O with a tetrahedral center
like methane. On test day, linear molecules always show 180° angles regardless of resonance
forms.
Question 3 of 50
A clinician prepares an intravenous saline solution by dissolving 9.0 g of NaCl in enough
water to make 1.0 L of solution. What is the approximate osmolarity of this physiological
saline solution?
A. 0.077 Osm
B. 0.154 Osm
C. 0.617 Osm
D. 0.308 Osm ✓ CORRECT
Correct Answer: D
Rationale: Physiological saline contains 9 g NaCl per liter; dividing by 58.4 g/mol gives 0.154
mol, and since NaCl dissociates into two particles, the osmolarity is 0.308 Osm. Choice B
represents the molarity but misses the van't Hoff factor of 2. On test day, always check
whether the question asks for molarity or osmolarity.
Question 4 of 50
A marathon runner's muscles metabolize glucose according to the overall reaction C6H12O6
+ 6O2 → 6CO2 + 6H2O with ΔH° = -2803 kJ/mol. How much heat is released when 18.0 g of
glucose is completely oxidized during intense exercise?
A. -280 kJ ✓ CORRECT
B. -467 kJ
C. -1402 kJ
D. -2803 kJ
Correct Answer: A
Rationale: Glucose has a molar mass of 180 g/mol, so 18.0 g equals 0.100 mol; multiplying
by -2803 kJ/mol gives approximately -280 kJ. Choice D fails to account for the mole-to-gram
conversion and simply uses the per-mole value. On test day, always verify whether the given
mass matches the molar mass before selecting the thermochemical value.
Question 5 of 50
In a study of acetylcholinesterase kinetics, the enzyme catalyzes the hydrolysis of
acetylcholine. The following initial rate data were collected:
, [Acetylcholine] (mM) | Initial Rate (mM/s)
0.10 | 2.0 × 10⁻³
0.20 | 4.0 × 10⁻³
0.30 | 6.0 × 10⁻³
What is the order of reaction with respect to acetylcholine?
A. Zero
B. Second
C. First ✓ CORRECT
D. Third
Correct Answer: C
Rationale: Doubling the substrate concentration from 0.10 to 0.20 mM exactly doubles the
initial rate, and tripling it triples the rate, indicating a first-order dependence. Choice B would
require the rate to quadruple when the concentration doubles, which does not match the
data. On test day, check rate ratios against concentration ratios to determine reaction order
quickly.
Question 6 of 50
A patient with chronic obstructive pulmonary disease experiences elevated blood CO2 levels,
shifting the bicarbonate buffer equilibrium: CO2 + H2O ⇌ H2CO3 ⇌ H⁺ + HCO3⁻. According to
Le Châtelier's principle, what happens to the concentration of bicarbonate when arterial CO2
rises?
A. It decreases because the equilibrium shifts left.
B. It increases because the equilibrium shifts right. ✓ CORRECT
C. It remains unchanged because buffers resist all change.
D. It decreases because H⁺ reacts with bicarbonate.
Correct Answer: B
Rationale: Adding CO2, a reactant, drives the equilibrium to the right, producing more H⁺ and
HCO3⁻; thus bicarbonate concentration rises. Choice A confuses the direction of shift,
forgetting that adding a reactant pushes the reaction toward products. On test day, trace the
added species as a reactant or product before predicting the shift.
Question 7 of 50
A pharmacist prepares a buffer for an ophthalmic solution using acetic acid (pKa = 4.76) and
sodium acetate. If the buffer contains equal concentrations of acetic acid and acetate, what
is the approximate pH?
A. 3.76
B. 4.26
Biological Systems Prep Pack Exam Official
Practice Exam Actual Exam 2026/2027 with
Detailed Rationales | Complete Exam-Style
Questions | Pass Guaranteed – A+ Graded
══════════════════════════════════════
SECTION 1: GENERAL CHEMISTRY Q1 – Q13
══════════════════════════════════════
Question 1 of 50
A patient with hyperthyroidism receives radioactive iodine-131 therapy. I-131 decays by
emitting a beta particle. If a neutral I-131 atom undergoes this decay, what is the resulting
ion's charge?
A. -1
B. 0
C. +1 ✓ CORRECT
D. +2
Correct Answer: C
Rationale: Beta decay converts a neutron to a proton and an electron; the electron is emitted,
leaving the nucleus with one extra proton and the same electron count, yielding a +1 cation.
Choice A incorrectly assumes the emitted electron remains with the atom. On test day,
remember that beta particles are emitted, not retained.
Question 2 of 50
A researcher is studying the anesthetic gas nitrous oxide (N2O) used in dental procedures. In
the most stable Lewis structure of N2O, what is the approximate bond angle at the central
nitrogen atom?
A. 90°
B. 180° ✓ CORRECT
C. 109.5°
D. 120°
,Correct Answer: B
Rationale: The most stable resonance structure of N2O has a linear geometry with the central
N sp-hybridized, giving a 180° bond angle. Choice C confuses N2O with a tetrahedral center
like methane. On test day, linear molecules always show 180° angles regardless of resonance
forms.
Question 3 of 50
A clinician prepares an intravenous saline solution by dissolving 9.0 g of NaCl in enough
water to make 1.0 L of solution. What is the approximate osmolarity of this physiological
saline solution?
A. 0.077 Osm
B. 0.154 Osm
C. 0.617 Osm
D. 0.308 Osm ✓ CORRECT
Correct Answer: D
Rationale: Physiological saline contains 9 g NaCl per liter; dividing by 58.4 g/mol gives 0.154
mol, and since NaCl dissociates into two particles, the osmolarity is 0.308 Osm. Choice B
represents the molarity but misses the van't Hoff factor of 2. On test day, always check
whether the question asks for molarity or osmolarity.
Question 4 of 50
A marathon runner's muscles metabolize glucose according to the overall reaction C6H12O6
+ 6O2 → 6CO2 + 6H2O with ΔH° = -2803 kJ/mol. How much heat is released when 18.0 g of
glucose is completely oxidized during intense exercise?
A. -280 kJ ✓ CORRECT
B. -467 kJ
C. -1402 kJ
D. -2803 kJ
Correct Answer: A
Rationale: Glucose has a molar mass of 180 g/mol, so 18.0 g equals 0.100 mol; multiplying
by -2803 kJ/mol gives approximately -280 kJ. Choice D fails to account for the mole-to-gram
conversion and simply uses the per-mole value. On test day, always verify whether the given
mass matches the molar mass before selecting the thermochemical value.
Question 5 of 50
In a study of acetylcholinesterase kinetics, the enzyme catalyzes the hydrolysis of
acetylcholine. The following initial rate data were collected:
, [Acetylcholine] (mM) | Initial Rate (mM/s)
0.10 | 2.0 × 10⁻³
0.20 | 4.0 × 10⁻³
0.30 | 6.0 × 10⁻³
What is the order of reaction with respect to acetylcholine?
A. Zero
B. Second
C. First ✓ CORRECT
D. Third
Correct Answer: C
Rationale: Doubling the substrate concentration from 0.10 to 0.20 mM exactly doubles the
initial rate, and tripling it triples the rate, indicating a first-order dependence. Choice B would
require the rate to quadruple when the concentration doubles, which does not match the
data. On test day, check rate ratios against concentration ratios to determine reaction order
quickly.
Question 6 of 50
A patient with chronic obstructive pulmonary disease experiences elevated blood CO2 levels,
shifting the bicarbonate buffer equilibrium: CO2 + H2O ⇌ H2CO3 ⇌ H⁺ + HCO3⁻. According to
Le Châtelier's principle, what happens to the concentration of bicarbonate when arterial CO2
rises?
A. It decreases because the equilibrium shifts left.
B. It increases because the equilibrium shifts right. ✓ CORRECT
C. It remains unchanged because buffers resist all change.
D. It decreases because H⁺ reacts with bicarbonate.
Correct Answer: B
Rationale: Adding CO2, a reactant, drives the equilibrium to the right, producing more H⁺ and
HCO3⁻; thus bicarbonate concentration rises. Choice A confuses the direction of shift,
forgetting that adding a reactant pushes the reaction toward products. On test day, trace the
added species as a reactant or product before predicting the shift.
Question 7 of 50
A pharmacist prepares a buffer for an ophthalmic solution using acetic acid (pKa = 4.76) and
sodium acetate. If the buffer contains equal concentrations of acetic acid and acetate, what
is the approximate pH?
A. 3.76
B. 4.26
