Acid mucin is best demonstrated by the stain -
Mucin is produced by epithelial cells of mucous membrane & mucous glands, as well as by some connective tissues
Stains for mucin

Mucicarmine
Alcian blue.

Note :- Epithelial cell mucin stains positively with periodic acid-Schiff (PAS), while connective tissue mucin does not.
Alcian blue
Periodic Acid Schiff (P.A.S.)
Van Gieson
Reticulin