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

12th Grade > Chemistry

P BLOCK ELEMENTS MCQs

Total Questions : 30 | Page 2 of 3 pages

Question 11. Orthoboric acid when heated to red hot gives

Metaboric acid
Metaboric acid
Boron and water
Boric anhydride

Discuss Question

Answer: Option D. -> Boric anhydride
:
D

H_{3} B O_{3} 100^{\circ} C - -- \to H B O_{2} 160^{\circ} C - -- \to H_{2} B_{4} O_{7} + H_{2} O ↓ 2 B_{2} O_{3} + H_{2} O

Question 12. ....... is the by-product obtained in the Serpeck's process -

Oxygen
Ammonia
Nitrogen dioxide
Nitric oxide

Discuss Question

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 13. Treatment of concentrated solution of borax with calculated quantity of sulphuric acid gives

HBO2
H2B4O7
H3BO3
B2O3

Discuss Question

Answer: Option C. -> H3BO3
:
C

N a_{2} B_{4} O_{7} + H_{2} S O_{4} + 5 H_{2} O \to N a_{2} S O_{4} + 4 H_{3} B O_{3}

Question 14. Aqueous solution of borax reacts with two mol of acids. This is because of -

Formation of 2 mol of B(OH)3 only
Formation of 1mol of [B(OH)4]− only
Formation of 1 mol each of B(OH)3 and [B(OH)4]−
Formation of 2 mol each of [B(OH)4]− and B(OH)3, of which only[B(OH)4]− reacts with acid

Discuss Question

Answer: Option D. -> Formation of 2 mol each of [B(OH)4]− and B(OH)3, of which only[B(OH)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 15. Which of the following statements is true about element R present in

13^{t h}

group of the periodic table?

It is gas at room temperature.
It has oxidation state of + 4.
It forms R2O3.
It forms RX2.

Discuss Question

Answer: Option C. -> It forms R2O3.
:
C
Group 13 elements belong to the boron family. The oxidation state of group 13 elements is either +1 or +3. All the group 13 elements are solids at room temperature. Valency of element R present in

13^{t h}

group of the periodic table is 3. Hence it can form

R_{2} O_{3}

when it reacts with oxygen.

Question 16. 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 1100 and 930
The angle Al - Cl - Al is 870

Discuss Question

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-

In Al2Cl6, Which Statement Is Incorrect-

Question 17. 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

Discuss Question

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< BI3smaller atom shows more back bonding

Question 18.

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 -

Cu2O
CuS
CuSO3
Cu(BO2)2

Discuss Question

Answer: Option D. -> Cu(BO2)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 19. 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

Discuss Question

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

Question 20. Which species does not exist -