Kerala SSLC · Chemistry · Class 10

Gas Laws and Mole Concept: Important Questions with Answers

These are 10 important multiple-choice questions from the Kerala SSLC Chemistry chapter “Gas Laws and Mole Concept” (Kerala SCERT syllabus). Each one shows the correct answer and a short explanation of why it is right. Try answering before you read the answer. ExamSummary has 10 practice questions on this chapter in total.

  1. Q1.What is the number of moles present in 11 grams of carbon dioxide (CO₂)? (Atomic masses: C=12, O=16)

    • A)0.25 mol
    • B)0.5 mol
    • C)1.0 mol
    • D)2.0 mol

    Answer: A) 0.25 mol

    The molar mass of CO₂ is calculated as 12 + (2 × 16) = 44 g/mol. Dividing the given mass of 11 g by the molar mass gives 11/44 = 0.25 moles.

  2. Q2.According to Avogadro’s Law, at the same temperature and pressure, equal volumes of all gases contain equal numbers of what?

    • A)Atoms
    • B)Molecules
    • C)Electrons
    • D)Protons

    Answer: B) Molecules

    Avogadro’s Law states that equal volumes of gases under identical conditions contain an equal number of molecules, regardless of the gas type. This principle allows us to relate gas volume directly to the amount of substance in moles.

  3. Q3.What is the standard molar volume of an ideal gas at STP (Standard Temperature and Pressure)?

    • A)11.2 L
    • B)22.4 L
    • C)44.8 L
    • D)1.0 L

    Answer: B) 22.4 L

    At STP (0°C and 1 atm), one mole of any ideal gas occupies approximately 22.4 liters of volume. This is a standard constant used for converting between moles and volume in gas problems.

  4. Q4.Which gas law describes the relationship between pressure and volume when temperature is kept constant?

    • A)Charles’s Law
    • B)Gay-Lussac’s Law
    • C)Boyle’s Law
    • D)Avogadro’s Law

    Answer: C) Boyle’s Law

    Boyle’s Law states that pressure and volume are inversely proportional at constant temperature (P ∝ 1/V). As volume decreases, pressure increases, provided the temperature remains unchanged.

  5. Q5.If 2 moles of hydrogen gas occupy 44.8 L at STP, what volume will 1 mole of oxygen gas occupy at the same conditions?

    • A)11.2 L
    • B)22.4 L
    • C)44.8 L
    • D)89.6 L

    Answer: B) 22.4 L

    According to Avogadro's Law, the volume depends only on the number of moles at constant T and P. Therefore, 1 mole of any gas at STP occupies 22.4 L, independent of the gas identity.

  6. Q6.Calculate the molecular mass of Calcium Carbonate (CaCO₃). (Atomic masses: Ca=40, C=12, O=16)

    • A)84 u
    • B)100 u
    • C)120 u
    • D)60 u

    Answer: B) 100 u

    The molecular mass is calculated by summing the atomic masses: 40 (Ca) + 12 (C) + 3×16 (O) = 40 + 12 + 48 = 100 u. This value represents the mass of one molecule in atomic mass units.

  7. Q7.Which of the following graphs correctly represents Boyle’s Law (Pressure vs Volume)?

    • A)Straight line through origin
    • B)Hyperbola curve
    • C)Parabolic curve
    • D)Horizontal straight line

    Answer: B) Hyperbola curve

    Boyle's Law implies an inverse relationship (PV = constant), which plots as a rectangular hyperbola on a P-V graph. A straight line would indicate direct proportionality, which is incorrect for this law.

  8. Q8.How many atoms are present in 0.5 moles of Helium gas (He)? (Avogadro’s number = 6.022 × 10²³)

    • A)3.011 × 10²³
    • B)6.022 × 10²³
    • C)1.204 × 10²⁴
    • D)3.011 × 10²²

    Answer: A) 3.011 × 10²³

    Helium is a monoatomic gas, so 1 mole contains 6.022 × 10²³ atoms. For 0.5 moles, multiply by 0.5, resulting in 3.011 × 10²³ atoms.

  9. Q9.What happens to the volume of a fixed mass of gas if its absolute temperature is doubled at constant pressure?

    • A)Volume halves
    • B)Volume doubles
    • C)Volume remains same
    • D)Volume quadruples

    Answer: B) Volume doubles

    Charles’s Law states that volume is directly proportional to absolute temperature (V ∝ T) at constant pressure. Therefore, doubling the Kelvin temperature results in doubling the volume.

  10. Q10.In the reaction N₂ + 3H₂ → 2NH₃, if 1 mole of Nitrogen reacts completely, how many moles of Ammonia are produced?

    • A)1 mole
    • B)2 moles
    • C)3 moles
    • D)0.5 moles

    Answer: B) 2 moles

    The balanced equation shows a stoichiometric ratio of 1:2 between Nitrogen and Ammonia. Thus, reacting 1 mole of N₂ yields exactly 2 moles of NH₃.

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