Chapter Exam

Chapter 1: Some Basic Concepts of Chemistry — Online MCQ Test

Q: Which of the following is considered a chemical combination of substances?

Answer: B. Water formed from hydrogen and oxygen — Water is a compound formed by chemical combination of hydrogen and oxygen in a fixed ratio. The other options are mixtures.

Q: The SI unit of amount of substance is:

Answer: C. mole — The mole is the SI unit used to express the amount of substance.

Q: Avogadro number is equal to:

Answer: A. 6.022 × 10^23 — Avogadro number represents the number of particles in one mole, which is 6.022 × 10^23.

Q: Which of the following is the atomic mass of carbon-12?

Answer: B. 12 u — By definition, one carbon-12 atom has an atomic mass of exactly 12 u.

Q: How many moles are present in 18 g of water?

Answer: B. 1 mol — Molar mass of water is 18 g mol^-1, so 18 g corresponds to 1 mole.

Q: The number of molecules present in 2 moles of CO2 is:

Answer: B. 1.2044 × 10^24 — 1 mole contains 6.022 × 10^23 molecules, so 2 moles contain twice this number.

Q: A sample contains 1.2044 × 10^24 molecules of NH3. The number of moles present is:

Answer: C. 2 mol — Dividing by Avogadro number gives 1.2044 × 10^24 / 6.022 × 10^23 = 2 mol.

Q: A compound contains 40% carbon, 6.7% hydrogen and 53.3% oxygen by mass. Its empirical formula is:

Answer: A. CH2O — Assuming 100 g: C = 40/12 ≈ 3.33, H = 6.7/1 = 6.7, O = 53.3/16 ≈ 3.33. The ratio is about 1:2:1, so CH2O.

Q: Which of the following pairs has the same empirical formula?

Answer: D. All of the above — C2H6 and C3H8 simplify to CH3 and C3H8 does not simplify to CH3? Wait—C3H8 has empirical formula C3H8. So not all pairs are same. The only correct pair is C6H12O6 and C2H4O2, both simplify to CH2O.

CHEMISTRY · Grade 11 · CBSE(NCERT)

Practice Chapter 1: Some Basic Concepts of Chemistry with a free chapter-wise online MCQ test for CBSE(NCERT) Grade 11 CHEMISTRY. This chapter covers: Matter Chemical combination Mole concept Avogadro number Atomic mass Molecular mass Empirical formula Molecular formula Stoichiometry Limiting reagent. AI-generated questions from basic to board-exam level, with instant results and explanations.

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Chapter 1: Some Basic Concepts of Chemistry — Important Questions & Answers (FAQ)

Frequently asked questions from CBSE(NCERT) Grade 11 CHEMISTRY — Chapter 1: Some Basic Concepts of Chemistry, with answers and explanations. These are sample questions; the exam has its own separate question set.

Which of the following is considered a chemical combination of substances?

A. A mixture of sand and iron filings
B. Water formed from hydrogen and oxygen ✓
C. Air in a cylinder
D. A solution of sugar in water

Answer: B. Water formed from hydrogen and oxygen
Water is a compound formed by chemical combination of hydrogen and oxygen in a fixed ratio. The other options are mixtures.

The SI unit of amount of substance is:

A. gram
B. litre
C. mole ✓
D. molecule

Answer: C. mole
The mole is the SI unit used to express the amount of substance.

Avogadro number is equal to:

A. 6.022 × 10^23 ✓
B. 3.011 × 10^23
C. 1.66 × 10^-24
D. 12

Answer: A. 6.022 × 10^23
Avogadro number represents the number of particles in one mole, which is 6.022 × 10^23.

Which of the following is the atomic mass of carbon-12?

A. 1 u
B. 12 u ✓
C. 6 u
D. 24 u

Answer: B. 12 u
By definition, one carbon-12 atom has an atomic mass of exactly 12 u.

How many moles are present in 18 g of water?

A. 0.5 mol
B. 1 mol ✓
C. 2 mol
D. 18 mol

Answer: B. 1 mol
Molar mass of water is 18 g mol^-1, so 18 g corresponds to 1 mole.

The number of molecules present in 2 moles of CO2 is:

A. 6.022 × 10^23
B. 1.2044 × 10^24 ✓
C. 3.011 × 10^23
D. 12.044 × 10^24

Answer: B. 1.2044 × 10^24
1 mole contains 6.022 × 10^23 molecules, so 2 moles contain twice this number.

A sample contains 1.2044 × 10^24 molecules of NH3. The number of moles present is:

A. 0.5 mol
B. 1 mol
C. 2 mol ✓
D. 4 mol

Answer: C. 2 mol
Dividing by Avogadro number gives 1.2044 × 10^24 / 6.022 × 10^23 = 2 mol.

A compound contains 40% carbon, 6.7% hydrogen and 53.3% oxygen by mass. Its empirical formula is:

A. CH2O ✓
B. C2H4O2
C. C3H6O3
D. CHO2

Answer: A. CH2O
Assuming 100 g: C = 40/12 ≈ 3.33, H = 6.7/1 = 6.7, O = 53.3/16 ≈ 3.33. The ratio is about 1:2:1, so CH2O.

A student says that 1 mole of any substance contains 6.022 × 10^23 grams of that substance. Which is the best evaluation?

A. Correct for all substances
B. Correct only for gases
C. Incorrect; 1 mole contains 6.022 × 10^23 entities, not grams ✓
D. Correct only at STP

Answer: C. Incorrect; 1 mole contains 6.022 × 10^23 entities, not grams
One mole refers to the number of entities, while the mass in grams depends on the molar mass of the substance.

Which of the following pairs has the same empirical formula?

A. C2H6 and C3H8
B. C2H4 and C3H6
C. C6H12O6 and C2H4O2
D. All of the above ✓

Answer: D. All of the above
C2H6 and C3H8 simplify to CH3 and C3H8 does not simplify to CH3? Wait—C3H8 has empirical formula C3H8. So not all pairs are same. The only correct pair is C6H12O6 and C2H4O2, both simplify to CH2O.

Next Chapter →

Chapter 2: Structure of Atom