What is mustard gas ?

Cl_(2) is used in the preparation of poisonous gases, one of them is mustard gas, which can be represented by the formula

Cl_(2) is used preparation of poisonous gases, one of them is mustard gas, which can be represented by the formula

Mustard gas is:

A halogen (x) reacts with sulphur gives a compound (y) .(y) reacts with ethylene to give Mustard gas . Then

What is formula of mustard gas-