Which of the following aromatic compounds undergoes sulphonation reaction most easily?

Nitrobenzene can be prepared from benzene by using a mixture of conc. $HNO_3$ and conc. $H_2SO_4$. In the mixture,nitric acid acts as a/an

Identify the heteroatom and the number of double bonds present in furan,respectively.

The increasing order of reactivity of the following compounds towards aromatic electrophilic substitution reaction is:

Among the following,the number of aromatic compound$(s)$ is

$A$ and $B$ are isomers. Product $B$ is: (Dewar's Benzene is $A$)