P Block Elements(11th And 12th > Chemistry ) Questions and answers for exam Preparation

Question 1.

$C a_{2} B_{6} O_{11} + N a_{2} C O_{3} F u s e d - -- \to (A) + (B) + C a C O_{3} (A) + C O_{2} \to (B) + N a_{2} C O_{3} Solution (B) + C o n c . H C I \to N a C I + A c i d ↓ H_{2} O (C) S t r o n g l y - ---- \to h e a t e d (D) Acid (C) (D) + C u S O_{4} H e a t e d - ---- \to i n f l a m e Blue coloured (E) compound compound (E) is -$

$C u_{2} O$
$C u S$
$C u S O_{3}$
$C u (B O_{2})_{2}$

Explanation:-

Answer: Option D. ->

C u (B O_{2})_{2}

:
D

Compound (A) is - $N a B O_{2}$
Compound (B) is - $N a_{2} B_{4} O_{7}$
Compound (C) is - $H_{3} B O_{3}$
Compound (D) is - $B_{2} O_{3}$
Compound (E) is - $C u (B O_{2})_{2}$

Question 2.

....... is the by-product obtained in the Serpeck's process -

Oxygen
Ammonia
Nitrogen dioxide
Nitric oxide

Explanation:-

Answer: Option B. -> Ammonia
:
B

Serpeck's process involves -

$A l_{2} O_{3} + 3 C + N_{2} \to 2 A l N + 3 C O A l N + 3 H_{2} O \to A l (O H)_{3} ↓ + N H_{3} 2 A l (O H)_{3} Δ - \to A l_{2} O_{3} + 3 H_{2} O$

Question 3.

Aqueous solution of borax reacts with two mol of acids. This is because of -

Formation of 2 mol of $B (O H)_{3}$ only
Formation of 1mol of $[B (O H)_{4}]^{-}$ only
Formation of 1 mol each of $B (O H)_{3}$ and $[B (O H)_{4}]^{-}$
Formation of 2 mol each of $[B (O H)_{4}]^{-}$ and $B (O H)_{3}$ , of which only $[B (O H)_{4}]^{-}$ reacts with acid

Explanation:-

Answer: Option D. -> Formation of 2 mol each of

[B (O H)_{4}]^{-}

and

B (O H)_{3}

, of which only

[B (O H)_{4}]^{-}

reacts with acid
:
D

$N a_{2} B_{4} O_{7} + 7 H_{2} O \to 2 B (O H)_{3} + 2 N a [B (O H)_{4}]$

$B (O H)_{3} o r H_{3} B O_{3}$ is an acid and does not react with acid.

Hence $N a [B (O H)_{4}]$ reacts with acid.

Question 4.

The main factor responsible for weak acidic nature of B-F bonds in BF3 is -

Large electronegativity of F
Three centred two electron bonds in BF3
pp- dp back bonding
pp- pp back bonding

Explanation:-

Answer: Option D. -> pp- pp back bonding
:
D

It is pp- pp bonding involving B and F atom responsible for the acidic nature of boron halides as BF3<BCl3<BBr3< BI3 smaller atom shows more back bonding

Question 5.

In $A l_{2} C l_{6}$ , which statement is incorrect-

Four Al - Cl bonds are of same length and two of different length
Six Al - Cl bonds are of same length and two of different length
The angle Cl - Al - Cl is $110^{0}$ and $93^{0}$
The angle Al - Cl - Al is $87^{0}$

Explanation:-

Answer: Option A. -> Four Al - Cl bonds are of same length and two of different length
:
A

$A I_{2} C I_{6}$ has the structure given below-

Question 6.

An aqueous solution of potash alum is -

Acidic
Alkaline
Neutral
None of these

Explanation:-

Answer: Option A. -> Acidic
:
A

$K_{2} S O_{4} . A I_{2} (S O_{4})_{3} . 24 H_{2} O K_{2} S O_{4} + H_{2} O \to K (O H) + H_{2} S O_{4} A I_{2} (S O_{4})_{3} + H_{2} O \to A l (O H)_{3} + H_{2} S O_{4}$

Question 7.

Thallium shows different oxidation states because -

It is a transition metal
Of inert pair effect
Of its amphoteric character
Of its high reactivity

Explanation:-

Answer: Option B. -> Of inert pair effect
:
B

Inert pair effect is the phenomenon in which outer shell (ns2)electrons penetrate to
(n - 1) d electrons and thus becomes closer to nucleus and are more effectively pulled towards nucleus. This results in less availability of ns electrons for bonding. The inert pair effects begins when n = 4 and increases with increasing value of n.

Question 8.

Which species does not exist -

$[B F_{6}]^{3 -}$
$[A l F_{6}]^{3 -}$
$[G a F_{6}]^{3 -}$
$[I n F_{6}]^{3 -}$

Explanation:-

Answer: Option A. ->

[B F_{6}]^{3 -}

:
A

$B F_{6}^{3 -}$ does not exist because boron does not have vacant d-subshells

Question 9.

Aluminium vessels should not be washed with materials containing washing soda because:

Washing soda is expensive
Washing soda is easily decomposed
Washing soda reacts with aluminium to form soluble aluminate
Washing soda reacts with aluminium to from insoluble aluminium oxide

Explanation:-

Answer: Option C. -> Washing soda reacts with aluminium to form soluble aluminate
:
C

$2 N a O H + 2 A l + 2 H_{2} O \to 2 N a A l O_{2} + 3 H_{2}$

Question 10.

Al and Ga have nearly the same covalent radii because of:

Greater shielding effect of s-electrons of Ga atoms
Poor shielding effect of s-electrons of Ga atoms
Poor shielding effect of d-electrons of Ga atoms
Greater shielding effect of d-electrons of Ga atoms

Explanation:-

Answer: Option C. -> Poor shielding effect of d-electrons of Ga atoms
:
C

Due to poor shielding effect of d-electrons, nuclear attraction over valency electrons increases hence atomic size decreases