Paper me aa chuke hai...dhyam se pdna ....Chemistry Elements of p-Block: Groups 13,14,15,16,17 and 18

1.Graphite is a soft solid lubricant extremely difficult to melt. The reasong for this anomalous behavior is that graphite. (2003)
(1)is an alio tropic form of diamond
(2)has molecules of variable molecular masses like polymers
(3)has carbon atoms arranged in large plates of rings of strongly bound carbon atoms with weak interplate bonds.
(4)is a non-crystalline substance.
Ans.(1) 4HC/ + 02–> 2Cl2 + 2H20  cloud of white fumes.

2.Concentrated hydrochloric acid when kept in open air sometimes produces a cloud of white fumes. The explanation for it is that (2003)
(1)oxygen in air reacts with the emitted HC1 gas to form a cloud of chlorine gas
(2)Strong affinity of HC1 gas for moisture in air results in forming of droplets of liquid solution which appears like a cloudy smoke.
(3)due to strong affinity for water. Concentrated hydrochloric acid pulls moisture of air towards itself. This moisture forms droplets of water and hence the cloud.
(4)concentrated hydrochloric acid emits strongly smelling HC1 gas all the time.
Ans.(3) Layers are held together.

3..Glass is a (2003)
(1)super -cooled liquid 2) gel
(3)polymeric mixture
(4)micro-crystalline solid
Ans.(1) Glass is a transparent or translucent super cooled liquid.

4.For making good quality mirrors plates of float glass are used. These are obtained by floating molten glass over a liquid metal which does not solidify before glass. The metal used can be    (2003)
(1)tin           2) sodium
3) magnesium               4) mercury
Ans.(4) It is because mercury exists as liquid at room temperature.

5..Which among the following factors is the mostimportant in making fluorine the strongest oxidizing halogen?(2004)
(1)Electron affinity
(2)Bond dissociation energy
(3)Hydration enthalpy 4) Ionization enthalpy
Ans.(2) Lower dissociation energy of bonds in F2.