On reaction with acid,$4$-pyrone gives a very stable cationic product. Which of the following structures shows the protonation site in that product?

The number of nucleophiles in the following list is $CH_3NH_2$,$CH_3CHO$,$C_2H_4$,$CH_3SH$.

Classify the following species as Nucleophilic or Electrophilic:
$NO_2^+$,$OH^{-}$,$CH_3NH_2$,$NH_3$,$Br^{+}$,$CH_3-CO^{-}-CH_3$

The attacking (electrophilic) species in sulphonation of benzene is

Giving justification,categorise the following molecules/ions as nucleophile or electrophile: $HS^{-}, BF_{3}, C_{2}H_{5}O^{-}, (CH_{3})_{3}N:, \overset{+}{Cl}, CH_{3}-\overset{+}{C}=O, H_{2}N:^{-}, \overset{+}{N}O_{2}$

Which of the following is a nucleophile?