1. Species with same number of neutrons but different number of protons are called:
Answer: a [Reason:] Isotones are atoms of different elements having same number of neutrons but different atomic and mass numbers. For e.g., Boron-12 and Carbon-12 are isotones each having 7 neutrons.
2. Atomic number of a species is the number of:
c) Valence electrons
Answer: b [Reason:] Atomic number or the number of protons is the property that differentiates atoms of one species from another. For e.g., atomic numbers of Hydrogen and Helium are 1 and 2 respectively.
3. Oxygen gas is denser than Carbon Dioxide gas?
Answer: b [Reason:] At any specified temperature, molar volume for every gas is the same. However CO2(g) has higher molar weight than O2(g) which results in higher density.
4. Which of the following has the least number of atoms?
a) One gram of Hydrogen gas
b) One gram of Helium gas
c) One gram-mole of Oxygen gas
d) One gram-mole of Chlorine gas
Answer: b [Reason:] One gram-mole of any gas contains Avogadro’s number of atoms/molecules. Hence, one gram-mole of Hydrogen gas and Helium gas weigh two grams and three grams respectively. 1g H2 = 1/2 g-mol H2; 1g He = 1/3 g-mol He. Thus, one gram of Helium has the least number of atoms.
5. Which of the following is not a pure form of matter?
d) Both Compound and Solution
Answer: c [Reason:] Different samples of the same element or compound will have exactly same composition and hence both – element and compound are considered pure forms of matter.
6. Which if the following is not an SI unit?
c) Atomic Mass Unit
Answer: c [Reason:] Because the SI unit of mass is kilogram.
7. One unified atomic mass unit equals:
a) 1/12 of molar mass of Carbon
b) 1/16 of atomic mass of Oxygen
c) molecular mass of Hydrogen
d) all of the mentioned
Answer: b [Reason:] 1 amu = 1/12 of atomic( not molar) mass of carbon = 1/16 of atomic mass of Oxygen = 1/2 of molecular mass of Hydrogen
8. Avogadro’s number of water molecules occupy 22.4 litre of space at 273 K.
Answer: b [Reason:] Molar volume at 273 K is 22.4 litre, only for gases. However, at this temperature water does not exist as gas.
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