Given below are two statements: 

The pK_a of HCN is 9.30. The pH of a solution prepared by mixing 2.5 moles of KCN and 2.5 moles of HCN in water and making up the total volume to 500 ml will be:

The basic buffer solution among the following is: 

1. ${\mathrm{NH}}_4\mathrm{Cl}+{\mathrm{NH}}_4\mathrm{OH}$

2. $\mathrm{NaCl}+\mathrm{NaOH}$

3. ${\mathrm{NH}}_4\mathrm{Cl}+{\mathrm{CH}}_3\mathrm{COOH}$

4. ${\mathrm{CH}}_3\mathrm{COONa}+{\mathrm{CH}}_3\mathrm{COOH}$

If the pH of an acidic buffer is 5.7 and ${\mathrm{pK}}_{\mathrm{a}}$ is 5 then the ratio of $\frac{\left[\mathrm{Salt}\right]}{\left[\mathrm{Acid}\right]}$ will be:

An acid buffer solution can be prepared by mixing the solutions of:

1. Sodium chloride and sodium hydroxide

2. Sulphuric acid and sodium sulphate

3. Ammonium chloride and ammonium nitrate

4. Ammonium acetate and acetic acid

The concentration of $\left[{\mathrm{H}}^{+}\right]$ ion in a solution containing 0.1 M HCN and 0.2 M NaCN will be:

(${\mathrm{K}}_{\mathrm{a}}$ for HCN = $6.2\times {10}^{-10}$)

1. 3.1$\times {10}^{10}$

2. $6.2\times {10}^5$

3.$$ $6.2\times {10}^{-10}$

4. $3.1\times {10}^{-10}$