Which of the following species is not stable?

1.	${\left[{\mathrm{SiCl}}_6\right]}^{2-}$	2.	${\left[{\mathrm{SiF}}_6\right]}^{2-}$
3.	${\left[{\mathrm{GeCl}}_6\right]}^{2-}$	4.	${\left[\mathrm{Sn}{\left(\mathrm{OH}\right)}_6\right]}^{2-}$

A compound is formed by cation C and anion A. The anions form hexagonal close packed (hcp) lattice and the cations occupy 75 % of octahedral voids. The formula of the compound is:

1. ${\mathrm{C}}_3{\mathrm{A}}_4$

2. ${\mathrm{C}}_2{\mathrm{A}}_3$

3. ${\mathrm{C}}_3{\mathrm{A}}_2$

4. ${\mathrm{C}}_4{\mathrm{A}}_3$

The correct structure of tribromo octoxide is:

1.
2.
3.
4.

The method used to remove the temporary hardness of water is-

1. Synthetic resins method

2. Calgon's method

3. Clark's method

4. Ion-exchange method

The non-essential amino acid among the following is:

Disproportionation reactions are:

For the chemical reaction ${\mathrm{N}}_2\left(\mathrm{(g)}\right)+3{\mathrm{H}}_2\left(\mathrm{(g}\right)$ )$\rightleftharpoons$ $2{\mathrm{NH}}_3\left(\mathrm{(g)}\right)$ the correct option is:

1. H₃O⁺ and H₂F⁺, respectively.

2. OH^– and H₂F⁺, respectively.

3. H₃O⁺ and F^–, respectively.

4. OH^– and F^–, respectively.

Grass leaves curl inwards during very dry weather. Select the most appropriate reason from the following :

1. Tyloses in vessels

2. Closure of stomata 

3. Flaccidity of bulliform cells

4. Shrinkage of air spaces in spongy mesophyll