The compound among the following with the lowest pK_a value is?

1. H₂O

2. H₂S

3. H₂Se

4. H₂Te

In diborane, the two H-B-H angles are nearly-

1. $60°,$ $120°$

2. $97°,120°$

3. $97°,150°$

4. $120°,$ $180°$

Among the following molecules, 

(i) $\stackrel{..}{X}e{O}_3$

(ii) $\stackrel{..}{X}eO{F}_4$

(iii) $\stackrel{..}{X}e{F}_6$

Those having the same number of lone pairs on Xe are

1. (i) and (ii) only

2. (i) and (iii) only

3. (ii) and (iii) only

4. (i), (ii) and (iii) only

A compound "X", upon reaction with H₂O, produces a colourless gas "Y" with a rotten fish smell.  Gas 'Y' is absorbed in a solution of CuSO₄ to give Cu₃P₂ as one of the products. The compound 'X' will be:

1. Ca₃P₂

2. ${\mathrm{NH}}_4\mathrm{Cl}$

3. ${\mathrm{As}}_2{\mathrm{O}}_3$

4. Ca₃(PO₄)₂

Aluminium chloride in acidified aqueous solution forms a complex 'A'.
The formula of A and hybridisation state of Al in 'A' is respectively:

1. [Al(H₂O)₆]³⁺, sp³d²

2. [Al(H₂O)₄]³⁺, sp³

3. [Al(H2O)4]3+, dsp2

4. [Al(H₂O)]³⁺, d²sp³

Incorrect order among the following is:

${\mathrm{H}}_3{\mathrm{BO}}_3$ is -

1. A Monobasic acid and a weak Lewis acid.

2. A Monobasic and a weak Bronsted acid..

3. A Monobasic and a strong Lewis acid.

4. A Tribasic and a weak Bronsted acid.

The basic structural unit of silicates is-

A solid (A) reacts with strong aqueous NaOH, liberating a foul smelling gas (B), which spontaneously burns in the air, giving smoky rings. A and B are, respectively:

1. P₄ (red) and PH₃ 

2. P₄ (white) and PH₃

3. S₈ and H₂S

4. P₄ (white) and H₂S

The incorrect statement among the following is -

1. ${\mathrm{PbX}}_2$ is more stable than ${\mathrm{PbX}}_4$

2. ${\mathrm{PbCl}}_4$ is less stable than ${\mathrm{SnCl}}_4$ but ${\mathrm{PbCl}}_2$ is more stable than ${\mathrm{SnCl}}_2$

3. ${\mathrm{PbCl}}_4$ is less stable than ${\mathrm{SnCl}}_4$

4. Pb(II) is a good reducing agent while Sn(II) is not