Which acid is present in ant sting that causes burning sensation and itching?

Bee sting leaves an acid which causes pain and irritation. The acid released is

Which one among the following is present in the nettle leaf hairs that causes burning pain ?

Which among the following acids is present in human stomach to aid the digestion of food?

Which of the following is present in maximum amount in acid rain?

Which chemical compound is present in Bleaching Powder?