The attacking (electrophilic) species in sulphonation of benzene is

Which of the following is an electrophile?

Which of the following species acts as an electrophile?

The cyanide ion $(CN^-)$ acts as an ambident nucleophile. From which end does it act as a stronger nucleophile in an aqueous medium? Give a reason for your answer.

$(a)$ Explain the following terms and provide the difference between them:
$(i)$ Reagent species
$(ii)$ Substrate species
$(b)$ $(i)$ What is the mechanism of a reaction?
$(ii)$ What are the uses of a reaction mechanism?
$(c)$ Depict the general reaction that occurs between a substrate and a reagent in an organic reaction.

The attacking or reactive electrophilic species in the nitration of benzene with concentrated $HNO_3$ and $H_2SO_4$ is: