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The p-Block Elements

Multiple Choice Questions

91.

C-C bond length is maximum in

diamond
graphite
naphthalene
fullerone

92.

Dry ice is

Solid H₂O
Solid CO₂
Solid N₂O₄
Solid NH₃

93.

When borax is heated strongly, it gives

BaBO₂
B₂O₃
B₃N₃H₆
Na₂B₄O₇

94.

Sindhur, an oxide of lead, is an example of ............. oxide.

basic
super
mixed
amphoteric

95.

The magnetic nature of boron molecule is same as the magnetic nature of

nitrogen molecule
carbon molecule
unipositive nitrogen molecule
oxide ion

96.

Which of the following is not a true alum?

Na₂SO₄.Al₂(SO₄)₃.24H₂O
MgSO₄.Cr₂(SO₄)₃.24H₂O
K₂SO₄.Cr₂(SO₄)₃.24H₂O
(NH₄)₂SO₄.Fe(SO₄)₃.24H₂O

97.

The densities of graphite and diamond at 298 K are 2.25 and 3.31 g cm^-3 respectively. If the standard free energy difference is 1895 J mol^-1, the pressure at which graphite will be transformed into diamond is

9.92 × 10⁸ Pa
9.92 × 10⁷ Pa
9.92 × 10⁶ Pa
None of these

98.
Which one of the following elements does not form triiodide on reacting with iodine?

B

Ti

Al

Ga

Boran show consistently +3 oxidation state in its compounds while rest of the elements show +1 as well as +3 oxidation states. The +1 oxidation state becomes more and more stable as we move down the group, i.e

Al < Ga < In < Ti

Thus is due to the presence of intervening d- and f-orbitals which do not shield the nucleus effectively. Consequently effective nuclear charge increases, that holds the ns-electrons tightly so that they do not participate in bonding(inert pair effect).

Due to inert pair effect, Ti in +1 oxidation state is more stable than that of +3 oxidation state.