The structural formula of ethyne is:

$(a)$ Complete the following equations:
$(i)$ $CH_4 + 2O_2 \longrightarrow CO_2 + 2H_2O + \text{Heat} + \text{Light}$
$(ii)$ $CH_3COOH + C_2H_5OH \xrightarrow{\text{Acid}} CH_3COOC_2H_5 + H_2O$
$(iii)$ $CH_3CH_2OH \xrightarrow[\text{443 K}]{\text{Conc. } H_2SO_4} CH_2=CH_2 + H_2O$

Vinegar is a solution of :

$CH_{3}COOCH_{3}$ is the molecular formula of which compound?

Give the formula and name of the alkane which contains four carbon atoms in each molecule.

Explain the following reactions with chemical equations:
$(i)$ Oxidation
$(ii)$ Hydrogenation
$(iii)$ Substitution