Dormin is a

The correct option is abscisic acid.

Abscisic acid (ABA) is a plant hormone that regulates various growth and development processes, including bud dormancy and stress responses.
In the 1960s, scientists studying bud dormancy isolated a substance responsible for inducing dormancy in deciduous trees. They named this substance "dormin".
Around the same time, another group of researchers isolated a substance that promotes the abscission of leaves and called it "abscisin II".
Subsequent chemical characterization and structural analysis revealed that dormin and abscisin II were chemically identical. The compound was thereafter officially named abscisic acid.
Therefore, dormin is another name for abscisic acid.