Sn crumbles to a powder in very cold weather, due to –

1. Expansion of the crystal lattice

2. Formation of SnO at low temperature

3. The conversion of Sn to powdery meta stannic acid

4. The transition from white tin to grey form, that is amorphous

Boric acid is polymeric because of:

1. Its acidic nature

2. Presence of hydrogen bonds

3. Its monobasic nature

4. Its geometry

Orthoboric acid when heated to red hot gives-

Borax is prepared by treating boric acid with:

(1) $NaN{O}_3$

(2) NaCl

(3) $N{a}_{2}C{O}_3$

(4) $NaHC{O}_3$

The main factor responsible for weak acidic nature of  B-F bonds in $B{F}_3$ is:

(1) large electronegativity of F

(2) three centred two electrons bonds in $B{F}_3$

(3) px-$d\mathrm{\pi }$ back bonding

(4) $p\mathrm{\pi }-\mathrm{p\pi }$ back bonding 

B-F bond order in $B{F}_3$ is:

(1) 1

(2) 2

(3) 3

(4) 4/3

Aluminium reacts with nitrogen to form:

1. AlN

2. $A{l}_2{N}_3$

3. $A{l}_{2}N$

4. $A{l}_4{N}_6$

Metal protected by a layer of its own oxide is:

(1) Al 

(2) Ag

(3) Au

(4) Cu

Which metal is powdered, suspended in oil and used as paint?

(1) Fe

(2) Sn

(3) Ag

(4) Al

Aluminium metal is corroded in coastal  places near to the sea, because protective oxide film:

(1) is removed by sea water

(2) reacts with sea water

(3) is attacked by salts present in sea water

(4) reacts with sand particles