c) i) An ionic bond is formed by the electrostatic attraction between oppositely charged ions, typically resulting from the complete transfer of electrons from a metal atom to a non-metal atom. A covalent bond is formed by the sharing of electrons between two non-metal atoms. ii) The method used for determining the molar mass of a volatile liquid is the Victor Meyer method (or Dumas method). iii) One condition necessary for the formation of hydrogen bonds is that a hydrogen atom must be directly bonded to a highly electronegative atom such as nitrogen (N), oxygen (O), or fluorine (F). d) i) The energy cycle diagram combines the following reactions: 1. Complete combustion of methane: $CH_4(g) + 2O_2(g) \to CO_2(g) + 2H_2O(g)$, $\Delta H_1 = -890 \text{ kJ mol}^{-1}$ 2. Combustion of carbon monoxide: $CO(g) + \frac{1}{2}O_2(g) \to CO_2(g)$, $\Delta H_2 = -283 \text{ kJ mol}^{-1}$ 3. Incomplete combustion of methane (target reaction): $CH_4(g) + \frac{3}{2}O_2(g) \to CO(g) + 2H_2O(g)$, $\Delta H_{incomplete}$ The energy cycle diagram is: $$ \begin{array}{c} CH_4(g) + 2O_2(g) \\ \swarrow \Delta H_{incomplete} \quad \searrow \Delta H_1 \\ CO(g) + 2H_2O(g) + \frac{1}{2}O_2(g) \quad CO_2(g) + 2H_2O(g) \\ \downarrow \Delta H_2 \\ CO_2(g) + 2H_2O(g) \\ \end{array} $$ The diagram shows the initial state ($CH_4(g) + 2O_2(g)$) at the top, the final state ($CO_2