Step 1: Understanding the Concept:
Mustard gas is a historically significant chemical warfare agent, known for its blistering effects on skin and lungs.
It is technically a thioether and a synthetic organic compound.
Step 2: Key Formula or Approach:
Recall the common or IUPAC names of the given chemical formulas and match them to the known structure of mustard gas, which is a sulfur-containing compound (a thioether).
Step 3: Detailed Explanation:
Let's identify each chemical formula provided in the options:
(A) \(\text{COCl}_2\): This is the chemical formula for Phosgene, another poisonous gas used in chemical warfare, but it is not mustard gas.
(C) \(\text{CCl}_3\text{NO}_2\): This is the formula for Chloropicrin, a broad-spectrum antimicrobial, fungicide, herbicide, insecticide, and nematicide, also used historically as a tear gas.
(D) \(\text{CCl}_2\text{F}_2\): This is Dichlorodifluoromethane, widely known as Freon-12, a common chlorofluorocarbon (CFC) used as a refrigerant.
(B) \(\text{Cl} - \text{CH}_2 - \text{CH}_2 - \text{S} - \text{CH}_2 - \text{CH}_2 - \text{Cl}\): The IUPAC name for this compound is bis(2-chloroethyl) sulfide.
This specific structure, featuring a central sulfur atom bonded to two 2-chloroethyl groups, is the exact chemical structure of the notorious mustard gas.
Step 4: Final Answer:
Option (B) represents the correct chemical formula for mustard gas.