Which of the following on reaction with Grignards reagent followed by hydrolysis forms tertiary alcohol?

In an ionic solid anions are arranged in hcp array and cations occupy $\frac{2}{3}$ of octahedral voids.

What is the formula of ionic compound? [consider $\mathrm{A}=$ cation; $\mathrm{B}=$ anion]

For a certain reaction $\Delta \mathrm{H}=-225 \mathrm{~kJ}$ and $\Delta S=-150 \mathrm{JK}^{-1}$. Find the temperature so that $\Delta G$ is zero.

Calculate the ionisation constant of $0.08 \mathrm{~mol} \mathrm{dm}{ }^{-3}$ of a monobasic acid having $\mathrm{pH}=2$.