Which two of the following compounds belong to the same homologous series?
$C_{2}H_{6}O, C_{2}H_{6}O_{2}, C_{2}H_{6}, CH_{4}O$

Which enzyme or substance is responsible for the conversion of milk into curd?

List three physical properties of covalent compounds and give reason for each.

Look at the figure and answer the following questions:
$(a)$ If ethanol is used instead of ethanoic acid,would you expect the same change?
$(b)$ How can a solution of lime water be prepared in the laboratory?

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

$A$ carboxylic acid (molecular formula $C_{2}H_{4}O_{2}$) reacts with an alcohol in the presence of an acid catalyst to form a compound $'X'$. The alcohol on oxidation with alkaline $KMnO_{4}$ followed by acidification gives the same carboxylic acid $C_{2}H_{4}O_{2}$. Write the name and structure of $(i)$ carboxylic acid,$(ii)$ alcohol,and $(iii)$ the compound $'X'$.