Identify the reagent R used in following conversion?

tert-butyl bromide $\xrightarrow{\mathrm{R}}$ Isobutylene

Calculate the mass of ' Ca ' deposited at cathode by passing 0.8 ampere current through molten $\mathrm{CaCl}_2$ in 60 minutes. [Molar mass of $\mathrm{Ca}=40 \mathrm{~g} \mathrm{~mol}^{-1}$ ]

What is the expected value of $\Delta T_f$ for $1.25 \mathrm{~m} \mathrm{CaCl}_2$ solution if 1.25 m sucrose solution has $\Delta \mathrm{T}_{\mathrm{f}}$ value x K ?

Calculate Henry's law constant if solubility of gas in water at $25^{\circ} \mathrm{C}$ is $5.14 \times 10^{-4} \mathrm{~mol} \mathrm{dm}^{-3}$ and partial pressure of the gas is 0.75 bar above solution.