1. There are seventeen non-metals in the periodic table. Unlike metals in the same period, they have higher:
a) Atomic number
b) Atomic size
c) Electropositivity
d) All of the mentioned
Explanation: Non-metals are located at the right end of their respective periods. As we move from left to right in a period or from top to bottom in a group, atomic number increases. Due to increasing charge on the nucleus, atomic size also decreases on moving right in a period. This is also the reason of increasing electronegativity or decreasing electropositivity.
2. d-block elements generally show multiple oxidation states. An exception to this is:
a) Zinc
b) Mercury
c) Copper
d) None of the mentioned
Explanation: Due to a small increase in successive ionization enthalpies, most d-block elements exist in multiple oxidation states. However, Zn(I) compounds are very rare and the ion exists in a dimeric form.
3. Uranium and Thorium are two important elements in the nuclear power industry. In which block of the modern periodic table are they placed?
a) s-block
b) p-block
c) d-block
d) f-block
Explanation: Ground state Uranium and Thorium atoms have partially or totally empty 5f-orbitals. They are members of the actinide family and their naturally occurring isotopes are radioactive.
4. Moving down a group, which of the following properties generally diminishes?
a) Electronegativity
b) Metallic character
c) Atomic radius
d) Molar mass
Explanation: Due to the addition of one shell on moving down a group, the neighbourhood of the atom is better shielded by the electrons from an attractive pull of the nucleus.
5. Radon is the sixth member of group 18 of the modern periodic table. Unlike other members of this group, Radon:
a) is solid near room temperature
b) is radioactive
c) possess high chemical reactivity
d) all of the mentioned
Explanation: Radon is a radioactive noble-gas at room temperatures. It is one of densest gases and the only naturally occurring radioactive gas. However, its daughter nuclei are solids. Not many compounds of Radon are known.
6. Ionization energy decreases down the group. It is the energy required by an isolated gaseous atom to form an anion.
a) True
b) False
Explanation: Ionization energy is the energy required by an isolated gaseous atom to lose the least tightly bound electron to form a cation. It decreases down the group as atomic size increases.
7. Allotropes differ in which of the following properties:
a) Atomic Number
b) Atomic Mass
c) Crystal Structure
d) Electronegativity
Explanation: Allotropes are different crystalline structures of the same element. Hence, they have the same atomic number, atomic mass and electronegativity. For e.g., graphite and diamond are allotropes of carbon.
8. Co-ordination number of a crystalline solid is:
a) Number of particles in the unit cell
b) Number of nearest neighbours of a particle
c) Number of octahedral voids in a unit cell
d) Number of tetrahedral voids in a unit cell
Explanation: Coordination number of a crystal structure is the number of particles with which a given particle is in direct contact.
9. Packing efficiency of a crystal structure is the ratio of:
a) Volume occupied by particles to the total volume of the unit cell
b) Volume occupied by particles to that by voids
c) Total volume of the unit cell to the volume occupied by particles
d) Volume occupied by voids to that by particles
Explanation: Packing efficiency represents the fraction of the unit cell volume that is utilized to hold the particles.
10. HCP and BCC are called close-packed structures. Close packed structures have:
a) Highest packing efficiency
b) Highest void fraction
c) Highest density
d) All of the mentioned
Explanation: Due to the largest number of particles in a unit cell, close-packed structures have the highest packing efficiency and hence, lest void fraction. Density is NOT a property of the crystal structure but the substance and depends also on molar mass.