Which gas is produced during the process of fermentation that causes effervescence?

The name of the compound $CH_{3}-CH_{2}-CHO$ is

Write the chemical equations for the reactions of ethanoic acid with the following:
$(a)$ Sodium
$(b)$ Sodium hydroxide
$(c)$ Ethanol
Also,write the name of one main product for each reaction.

$A$ 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 $'X'$.

The correct structural formula of butanoic acid is

Unsaturated hydrocarbons produce a yellow flame with a large amount of black smoke when burnt in oxygen. Give the reason.