Today’s Chemistry MCQs

1. Which of the following molecules has zero dipole moment?

• A) NH₃
• B) H₂O
• C) CO₂
• D) SO₂

2. The molecular shape of ammonia (NH₃) is:

• A) Tetrahedral
• B) Trigonal planar
• C) Trigonal pyramidal
• D) Linear

3. The central atom in SF₆ undergoes which type of hybridisation?

• A) sp³
• B) sp³d
• C) sp³d²
• D) sp²d

4. Which of the following substances shows the strongest hydrogen bonding?

• A) H₂O
• B) NH₃
• C) HF
• D) CH₃OH

5. The bond order of the oxygen molecule (O₂) according to molecular orbital theory is:

• A) 1
• B) 1.5
• C) 2
• D) 2.5

1. Which of the following properties generally increases from left to right across a period in the periodic table?

• A) Atomic radius
• B) Metallic character
• C) Ionization enthalpy
• D) Reducing power

2. Which element has the maximum electron gain enthalpy?

• A) Fluorine
• B) Chlorine
• C) Oxygen
• D) Nitrogen

3. The correct order of increasing atomic radius among the following elements is:
O, F, N, C

• A) F < O < N < C
• B) C < N < O < F
• C) O < F < N < C
• D) N < O < F < C

4. The first ionization enthalpy of oxygen is less than that of nitrogen because:

• A) Oxygen has higher nuclear charge
• B) Oxygen has a larger atomic size
• C) Oxygen has paired electrons in p-orbitals
• D) Nitrogen has lower electronegativity

5. Which of the following elements shows variable oxidation states most commonly?

• A) Sodium
• B) Magnesium
• C) Aluminium
• D) Iron

1. The maximum number of electrons that can be accommodated in a shell with principal quantum number n = 4 is:

• A) 16
• B) 18
• C) 32
• D) 50

2. Which of the following sets of quantum numbers is not allowed?

• A) n = 3, l = 2, m = −2, s = +1/2
• B) n = 2, l = 1, m = 0, s = −1/2
• C) n = 3, l = 3, m = 1, s = +1/2
• D) n = 1, l = 0, m = 0, s = +1/2

3. The wavelength of radiation associated with an electron moving in the first orbit of hydrogen atom is given by:

• A) de Broglie equation
• B) Heisenberg uncertainty principle
• C) Pauli exclusion principle
• D) Hund’s rule

4. Which transition in the hydrogen atom corresponds to the emission of radiation of maximum wavelength?

• A) n = 4 → n = 3
• B) n = 3 → n = 2
• C) n = 2 → n = 1
• D) n = 5 → n = 1

5. Which of the following orbitals has a dumbbell shape?

• A) s-orbital
• B) p-orbital
• C) d-orbital
• D) f-orbital

1. How many significant figures are present in the measurement 0.004560?

• A) 3
• B) 4
• C) 5
• D) 6

2. The number of atoms present in 0.1 mole of sodium is approximately:

• A) 6.02 × 10²¹
• B) 6.02 × 10²²
• C) 6.02 × 10²³
• D) 3.01 × 10²³

3. What is the mass of one mole of electrons?
(Mass of one electron = 9.1 × 10⁻²⁸ g)

• A) 0.0055 g
• B) 0.00055 g
• C) 5.5 g
• D) 55 g

4. A compound contains 40% carbon, 6.7% hydrogen and 53.3% oxygen by mass. The empirical formula of the compound is:

• A) CH₂O
• B) C₂H₄O
• C) CHO
• D) C₂H₂O

5. Which of the following quantities has the same numerical value in SI and CGS systems?

• A) Length
• B) Mass
• C) Temperature
• D) Time

1. The number of moles of KMnO₄ required to oxidize 1 mole of Fe²⁺ ions in acidic medium is:

• A) 1/5
• B) 1/3
• C) 1/2
• D) 1

2. For a first-order reaction, if the rate constant is doubled, the half-life of the reaction will:

• A) Remain unchanged
• B) Become half
• C) Become double
• D) Become four times

3. Which of the following compounds undergoes SN1 reaction most readily?

• A) CH₃Cl
• B) C₂H₅Cl
• C) (CH₃)₃CCl
• D) C₆H₅CH₂Cl

4. Which of the following reagents converts an aldehyde directly into a primary alcohol?

• A) PCC
• B) KMnO₄
• C) NaBH₄
• D) Tollens’ reagent

5. Which of the following species is paramagnetic?

• A) Zn²⁺
• B) Cu⁺
• C) Fe³⁺
• D) Ni²⁺ (low spin)

1. At 25°C, the vapour pressure of pure water is 23.8 mm Hg. When a non-volatile solute is added, the vapour pressure becomes 22.6 mm Hg. The mole fraction of the solute in the solution is:

• A) 0.050
• B) 0.052
• C) 0.048
• D) 0.045

2. For a reaction, the half-life is independent of the initial concentration of the reactant. The order of the reaction is:

• A) Zero order
• B) First order
• C) Second order
• D) Pseudo-first order

3. Which of the following reactions proceeds via a free radical mechanism?

• A) Addition of HBr to propene (without peroxide)
• B) Nitration of benzene
• C) Chlorination of methane in sunlight
• D) Hydration of ethene

4. Which of the following compounds gives a positive iodoform test?

• A) Propanal
• B) Acetophenone
• C) Benzaldehyde
• D) Methanol

5. The coordination number and geometry of the complex [Ni(CO)₄] are respectively:

• A) 4, square planar
• B) 4, tetrahedral
• C) 6, octahedral
• D) 2, linear

1. A sample contains 3.01 × 10²³ molecules of a gas X. The mass of the sample is 16 g. The molecular mass of gas X is:

• A) 16 g mol⁻¹
• B) 24 g mol⁻¹
• C) 32 g mol⁻¹
• D) 48 g mol⁻¹

2. For a spontaneous process at constant temperature and pressure, which of the following conditions must be satisfied?

• A) ΔH < 0 and ΔS < 0
• B) ΔG < 0
• C) ΔG > 0
• D) ΔH = 0

3. Which of the following carbocations is the most stable?

• A) CH₃⁺
• B) CH₃–CH₂⁺
• C) (CH₃)₂CH⁺
• D) (CH₃)₃C⁺

4. When propene reacts with HBr in the presence of peroxide, the major product formed is:

• A) 1-bromopropane
• B) 2-bromopropane
• C) 1,2-dibromopropane
• D) 2,3-dibromopropane

5. What is the oxidation state of cobalt in the complex [Co(NH₃)₆]Cl₃?

• A) +1
• B) +2
• C) +3
• D) 0

1. How many moles of oxygen atoms are present in 11.2 L of carbon dioxide gas at STP?

• A) 0.25 mol
• B) 0.5 mol
• C) 1 mol
• D) 2 mol

2. Which reagent is used to distinguish between aldehydes and ketones?

• A) Fehling’s solution
• B) Tollens’ reagent
• C) Benedict’s solution
• D) Schiff’s reagent

3. Which of the following has the highest lattice energy?

• A) NaCl
• B) KCl
• C) MgO
• D) CaO

4. For a first-order reaction, the time required to complete 75% of the reaction is:

• A) t½
• B) 2t½
• C) 3t½
• D) t½ / 2

5. Which of the following compounds shows geometrical isomerism?

• A) Propene
• B) But-2-ene
• C) Ethyne
• D) Propane