Question

Select the correct statements from the following
A)
Aluminium liberates \( \mathrm{H_2} \) gas with dil.\( \mathrm{HCl} \) but not with aqueous \( \mathrm{NaOH} \).
B)
Formula of sodium metaborate is \( \mathrm{Na_3BO_3} \)
C)
Boric acid is a weak monobasic acid
D)
For thallium, +1 state is more stable than +3 state.

• A. A & B
• B. B & C
• C. C & D
• D. A & D

Hint:

Inert pair effect makes the lower oxidation state (+1) more stable in heavier p-block elements like thallium.

Answer 1

The Correct Option is C

Statement A: Incorrect.
Aluminium reacts with both dilute HCl and aqueous NaOH, liberating \( \mathrm{H_2} \) gas in both cases.
So this statement is false. Statement B: Incorrect.
The correct formula of sodium metaborate is \( \mathrm{NaBO_2} \), not \( \mathrm{Na_3BO_3} \).
So this statement is false. Statement C: Correct.
Boric acid \( \mathrm{H_3BO_3} \) acts as a weak monobasic Lewis acid.
This statement is true. Statement D: Correct.
Due to the inert pair effect, thallium shows +1 oxidation state as more stable than +3.
This statement is true. Conclusion: Only statements C and D are correct.