Consider the following data :

$\Delta_{f}H^{\circ}$ (methane, g) = $-X \; \text{kJ mol}^{-1}$

Enthalpy of sublimation of graphite = $Y \; \text{kJ mol}^{-1}$

Dissociation enthalpy of $H_2 = Z \; \text{kJ mol}^{-1}$

The bond enthalpy of C–H bond is given by :

The correct order of the rate of the reaction for the following reaction with respect to nucleophiles is :

${CH_3Br + Nu^- \longrightarrow CH_3Nu + Br^-}$

By usual analysis, 1.00 g of compound (X) gave 1.79 g of magnesium pyrophosphate. The percentage of phosphorus in compound (X) is : (nearest integer)

(Given, molar mass in g mol⁻¹: O = 16, Mg = 24, P = 31)