Identify the compound '$$\mathrm{A}$$' in the following sequence of reactions.

$$\text { A } \xrightarrow[\text { Dryether }]{\mathrm{C}_2 \mathrm{H}_3 \mathrm{MgBr}} \mathrm{B} \xrightarrow{\mathrm{H}_3 \mathrm{O}^{+}} \text {3-Methylpentan-3-0l }$$

A solution of nonvolatile solute is obtained by dissolving $$15 \mathrm{~g}$$ in $$200 \mathrm{~mL}$$ water has depression in freezing point $$0.75 \mathrm{~K}$$. Calculate the molar mass of solute if cryoscopic constant of water is $$1.86 \mathrm{~K} \mathrm{~kg} \mathrm{~mol}^{-1}$$.

For a reaction $$\mathrm{A}+\mathrm{B} \rightarrow$$ products $$\Delta \mathrm{H}$$ is $$-84.2 \mathrm{~kJ}$$ and $$\Delta \mathrm{S}$$ is $$-200 \mathrm{~J} \mathrm{~K}^{-1}$$. Calculate the highest value of temperature so that the reaction will proceed in forward direction.

The solubility product of $$\mathrm{PbCl}_2$$ at $$298 \mathrm{~K}$$ is $$3.2 \times 10^{-5}$$. What is its solubility in $$\mathrm{mol} \mathrm{dm}{ }^{-3}$$ ?