At 4^oC , ionic product of water (K\(\omega\)) is 10^-16 . At this temperature, a solution has pH = 7.5 . The nature of this solution at 4^oC will be 

1. Acidic 

2. Alkaline 

3. Neutral

4. Cannot be predicted 

pH of a saturated solution of $\mathrm{Ca}{\left(\mathrm{OH}\right)}_2$ is 9. The solubility product $\left({\mathrm{K}}_{\mathrm{sp}}\right)$ of $\mathrm{Ca}{\left(\mathrm{OH}\right)}_2$ is:

1. $0.5\times {10}^{-10}$

2. $0.5\times {10}^{-15}$

3. $0.25\times {10}^{-10}$

4. $0.125\times {10}^{-15}$