1. Oxygen gas is denser than Carbon Dioxide gas?
a) True
b) False
Explanation: 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.
2. 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
Explanation: 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.
3. Which of the following is not a pure form of matter?
a) Element
b) Compound
c) Solution
d) Both Compound and Solution
Explanation: Different samples of the same element or compound will have an exactly same composition and hence both – element and compound are considered pure forms of matter.
4. Which if the following is not an SI unit?
a) Kilogram
b) Mole
c) Atomic Mass Unit
d) Coulomb
Explanation: Because the SI unit of mass is a kilogram.
5. One unified atomic mass unit equals to ____________
a) 1/12 of molar mass of Carbon
b) 1/16 of atomic mass of Oxygen
c) 1/2 of the molecular mass of Hydrogen
d) all of the mentioned
Explanation: 1 amu = 1/12 of atomic(not molar) mass of carbon = 1/16 of the atomic mass of Oxygen = 1/2 of molecular mass of Hydrogen.
6. Avogadro’s number of water molecules occupy 22.4 liters of space at 273 K.
a) True
b) False
Explanation: Molar volume at 273 K is 22.4 liter, only for gases. However, at this temperature water does not exist as a gas.
7. In the wave-mechanical model of an atom, degenerate energy levels have:
a) Equal energy
b) Equal number of electrons
c) Same shape
d) Electrons with the same spin
Explanation: Degenerate energy levels have equal energy. In an atom, the orbitals in the same subshell are degenerate in absence of an external magnetic field.
8. Paired electrons in an atom have equal values of all of the four quantum numbers.
a) True
b) False
Explanation: According to Pauli’s exclusion principle, no two electrons in an atom can have all four quantum numbers equal. Paired electrons have opposite spins.
9. Protons attract electrons. Then why do electrons not fall on the nucleus?
a) Neutrons repel the electrons
b) Electrons in ground state cannot radiate energy
c) At very small distances, protons repel electrons
d) Inner electrons repel those in outer orbitals
Explanation: In the ground state, electrons form standing waves. Standing waves are those in which energy is not transferred. Hence, electrons are bound to revolve around the nucleus with constant potential energy.
10. Number of atomic orbitals in nth shell is:
a) n2
b) 2n2
c) 2n + 1
d) n − 1
Explanation: Every shell contains n2 orbitals and every orbital can accommodate a maximum of 2 electrons. Hence a maximum of 2n2 electrons can reside in nth shell.