Chemistry (School & UG)

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Chemistry (School & UG)

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The Chemistry (School & UG) category covers the fundamental to advanced concepts of Chemistry, structured to support Class 11–12 students, competitive exam aspirants, and undergraduate learners. The content emphasizes conceptual clarity, problem-solving skills, and strong alignment with NCERT and university syllabi.

In this category, you will study:

Physical Chemistry – atomic structure, thermodynamics, chemical kinetics, equilibrium, electrochemistry, and solutions
Organic Chemistry – basic principles, reaction mechanisms, hydrocarbons, functional groups, biomolecules, and polymers
Inorganic Chemistry – periodic trends, chemical bonding, coordination compounds, metallurgy, and s-, p-, d-, and f-block elements
Numerical problem-solving – formula-based calculations, mole concept, and graph-based questions
Reaction mechanisms and derivations with step-by-step explanations
Comparisons, trends, and exceptions important for exams
NCERT-based theory, supported by diagrams, tables, MCQs, assertion–reason questions, numericals, and PYQs

The content is designed to build strong foundations, improve analytical and quantitative skills, and prepare students for school examinations, competitive exams, and undergraduate assessments.

Develop a clear, logical, and application-oriented understanding of Chemistry to excel academically and confidently tackle problem-based and conceptual questions at both school and UG levels.

Analytical Techniques Inorganic Chemistry Organic Chemistry Physical Chemistry

Q. For the reaction 3H2(g) + N2(g) ⇌ 2NH3(g), if the temperature is decreased, what will be the effect on the equilibrium position?

A. Shift to the left
B. Shift to the right
C. No effect
D. Depends on pressure

Solution

If the reaction is exothermic, decreasing the temperature will shift the equilibrium to the right, favoring NH3 production.

Correct Answer: B — Shift to the right

Q. For the reaction 4H2(g) + 2O2(g) ⇌ 4H2O(g), what is the effect of increasing the temperature?

A. Shift to the left
B. Shift to the right
C. No change
D. Increase the rate of reaction

Solution

Increasing the temperature of an exothermic reaction shifts the equilibrium to the left, favoring the reactants.

Correct Answer: A — Shift to the left

Q. For the reaction A + B → C, if the enthalpy change ΔH is -150 kJ/mol, what can be inferred about the reaction?

A. It is exothermic.
B. It is endothermic.
C. It is at equilibrium.
D. It requires energy input.

Solution

A negative ΔH indicates that the reaction releases heat, thus it is exothermic.

Correct Answer: A — It is exothermic.

Q. For the reaction A + B ⇌ C + D, if ΔH = -150 kJ and ΔS = -200 J/K, what is the temperature at which the reaction becomes non-spontaneous?

A. 750 K
B. 750 °C
C. 300 K
D. 150 K

Solution

At equilibrium, ΔG = 0; ΔG = ΔH - TΔS = 0; T = ΔH/ΔS = 150,000 J / 200 J/K = 750 K.

Correct Answer: A — 750 K

Q. For the reaction A(g) + B(g) ⇌ C(g), if the pressure is decreased, what will happen to the equilibrium?

A. Shift to the right
B. Shift to the left
C. No change
D. Reaction stops

Solution

Decreasing the pressure will shift the equilibrium to the side with more moles of gas, which in this case is the right side (C).

Correct Answer: A — Shift to the right

Q. For the reaction CO(g) + 2H2(g) ⇌ CH3OH(g), if the pressure is increased, what will be the effect on the equilibrium position?

A. Shift to the left
B. Shift to the right
C. No effect
D. Depends on temperature

Solution

Increasing pressure shifts the equilibrium towards the side with fewer moles of gas, which is the right side (1 mole of CH3OH).

Correct Answer: B — Shift to the right

Q. For the reaction CO(g) + 2H2(g) ⇌ CH3OH(g), what happens if H2 is removed from the system?

A. Equilibrium shifts to the right
B. Equilibrium shifts to the left
C. No change occurs
D. Reaction stops

Solution

Removing H2 will shift the equilibrium to the left to produce more H2, according to Le Chatelier's Principle.

Correct Answer: B — Equilibrium shifts to the left

Q. For the reaction H2(g) + I2(g) ⇌ 2HI(g), if the temperature is increased and Kc decreases, what does this indicate about the reaction?

A. Exothermic
B. Endothermic
C. Reversible
D. Irreversible

Solution

A decrease in Kc with an increase in temperature indicates that the reaction is exothermic.

Correct Answer: A — Exothermic

Q. For the reaction N2(g) + 3H2(g) ⇌ 2NH3(g), what happens if H2 is removed from the system?

A. Equilibrium shifts to the right
B. Equilibrium shifts to the left
C. No change occurs
D. NH3 concentration increases

Solution

Removing H2 decreases its concentration, causing the equilibrium to shift to the left to produce more reactants and restore balance.

Correct Answer: B — Equilibrium shifts to the left

Q. For the reaction N2(g) + 3H2(g) ⇌ 2NH3(g), what happens if the concentration of NH3 is decreased?

A. Equilibrium shifts to the right
B. Equilibrium shifts to the left
C. No change
D. Reaction stops

Solution

Decreasing the concentration of NH3 will shift the equilibrium to the right to produce more NH3, according to Le Chatelier's Principle.

Correct Answer: A — Equilibrium shifts to the right

Q. For the reaction N2(g) + 3H2(g) ⇌ 2NH3(g), what is the effect of decreasing the volume of the container?

A. Shifts equilibrium to the right
B. Shifts equilibrium to the left
C. No effect on equilibrium
D. Increases the concentration of NH3

Solution

Decreasing the volume increases the pressure, and according to Le Chatelier's Principle, the equilibrium will shift to the side with fewer moles of gas, which is to the right in this case.

Correct Answer: A — Shifts equilibrium to the right

Q. For the reaction N2(g) + 3H2(g) ⇌ 2NH3(g), what will happen if H2 is removed?

A. Shift to the right
B. Shift to the left
C. No change
D. Reaction stops

Solution

Removing H2 will shift the equilibrium to the left to produce more reactants, according to Le Chatelier's Principle.

Correct Answer: B — Shift to the left

Q. For the reaction N2(g) + 3H2(g) ⇌ 2NH3(g), what will happen if NH3 is removed from the system?

A. Shift to the right
B. Shift to the left
C. No change
D. Reaction stops

Solution

Removing NH3 will shift the equilibrium to the right to produce more NH3, in accordance with Le Chatelier's Principle.

Correct Answer: A — Shift to the right

Q. For the reaction N2(g) + 3H2(g) ⇌ 2NH3(g), what will happen if the concentration of NH3 is decreased?

A. Shifts to the right
B. Shifts to the left
C. No effect
D. Reaction stops

Solution

Decreasing the concentration of NH3 will shift the equilibrium to the right to produce more NH3, according to Le Chatelier's Principle.

Correct Answer: A — Shifts to the right

Q. How does dilution affect a reaction at equilibrium involving aqueous solutions?

A. Shifts equilibrium to the right
B. Shifts equilibrium to the left
C. No effect on equilibrium
D. Increases the rate of reaction

Solution

Dilution decreases the concentration of reactants and products, and according to Le Chatelier's Principle, the equilibrium will shift to the left to produce more reactants.

Correct Answer: B — Shifts equilibrium to the left

Q. How does increasing temperature affect an exothermic reaction at equilibrium?

A. Shifts equilibrium to the right
B. Shifts equilibrium to the left
C. No effect on equilibrium
D. Increases the rate of reaction

Solution

For an exothermic reaction, increasing the temperature shifts the equilibrium to the left, favoring the reactants, as the system tries to absorb the added heat.

Correct Answer: B — Shifts equilibrium to the left

Q. How does increasing temperature affect the enthalpy of a substance?

A. It decreases enthalpy.
B. It increases enthalpy.
C. It has no effect.
D. It depends on the substance.

Solution

Increasing temperature generally increases the enthalpy of a substance due to increased kinetic energy.

Correct Answer: B — It increases enthalpy.

Q. How does increasing temperature generally affect the enthalpy of a system?

A. It decreases the enthalpy
B. It has no effect on enthalpy
C. It increases the enthalpy
D. It depends on the type of reaction

Solution

Increasing temperature typically increases the enthalpy of a system due to the increased kinetic energy of the molecules.

Correct Answer: C — It increases the enthalpy

Q. How does increasing the temperature affect the equilibrium constant (K) of an endothermic reaction?

A. K decreases
B. K increases
C. K remains constant
D. K becomes zero

Solution

For an endothermic reaction, increasing the temperature increases the equilibrium constant (K) as the reaction favors the formation of products.

Correct Answer: B — K increases

Q. How does the addition of an inert gas at constant volume affect the equilibrium of a reaction?

A. Shifts equilibrium to the right
B. Shifts equilibrium to the left
C. No effect on equilibrium
D. Increases the reaction rate

Solution

Adding an inert gas at constant volume does not change the partial pressures of the reactants or products, thus having no effect on the equilibrium position.

Correct Answer: C — No effect on equilibrium

Q. How many grams of sodium chloride are needed to prepare 0.5 L of a 0.2 M solution?

A. 5.84 g
B. 11.68 g
C. 2.92 g
D. 0.58 g

Solution

Molar mass of NaCl = 58.44 g/mol. Moles needed = 0.2 M * 0.5 L = 0.1 moles. Mass = moles * molar mass = 0.1 * 58.44 g = 5.844 g.

Correct Answer: B — 11.68 g

Q. How many moles of potassium hydroxide are needed to neutralize 0.1 moles of hydrochloric acid?

A. 0.05
B. 0.1
C. 0.2
D. 0.3

Solution

The reaction between KOH and HCl is 1:1. Therefore, 0.1 moles of HCl will require 0.1 moles of KOH.

Correct Answer: B — 0.1

Q. How many stereoisomers can 2,3-dimethylbutane have?

A. 2
B. 4
C. 8
D. 16

Solution

2,3-dimethylbutane has no chiral centers, so it has only 1 stereoisomer.

Correct Answer: A — 2

Q. How many stereoisomers can 2-pentene have?

A. 0
B. 1
C. 2
D. 4

Solution

2-pentene has two geometric isomers: cis-2-pentene and trans-2-pentene.

Correct Answer: C — 2

Q. How many stereoisomers does 1,2-dichloropropane have?

A. 1
B. 2
C. 3
D. 4

Solution

1,2-dichloropropane has one chiral center, leading to 2 stereoisomers.

Correct Answer: B — 2

Q. If 1 mole of NaCl is dissolved in water, how many particles are present in solution?

A. 1
B. 2
C. 3
D. 4

Solution

1 mole of NaCl dissociates into 2 particles (1 Na⁺ and 1 Cl⁻), so there are 2 particles in solution.

Correct Answer: B — 2

Q. If 25 mL of 0.5 M acetic acid is mixed with 25 mL of 0.5 M sodium acetate, what is the resulting pH of the buffer solution?

A. 4.76
B. 5.00
C. 5.76
D. 6.00

Solution

Using the Henderson-Hasselbalch equation: pH = pKa + log([A-]/[HA]). pKa of acetic acid is approximately 4.76. Since [A-] = [HA], pH = 4.76.

Correct Answer: A — 4.76

Q. If 50 mL of 0.1 M sulfuric acid is neutralized by sodium hydroxide, how many moles of NaOH are required?

A. 0.005
B. 0.01
C. 0.02
D. 0.03

Solution

H2SO4 dissociates to give 2 H+ ions. Moles of H2SO4 = 0.1 M * 0.050 L = 0.005 moles. Therefore, moles of NaOH required = 0.005 moles * 2 = 0.01 moles.

Correct Answer: B — 0.01

Q. If a catalyst is added to the reaction A + B ⇌ C + D, what is the effect on the equilibrium position?

A. Shift to the left
B. Shift to the right
C. No change
D. Increase the rate of reaction

Solution

A catalyst speeds up the rate of both the forward and reverse reactions equally, thus having no effect on the position of the equilibrium.

Correct Answer: C — No change

Q. If a compound has a molar absorptivity of 200 L/(mol·cm) and a concentration of 0.01 mol/L, what is the absorbance at a path length of 1 cm?

A. 0.2
B. 2
C. 20
D. 0.02

Solution

Using Beer-Lambert Law (A = εlc), A = 200 L/(mol·cm) * 0.01 mol/L * 1 cm = 2.

Correct Answer: A — 0.2

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