Which one of the following chemical agent is not being used for dry-cleaning of clothes?

We start by recalling the basic principle of dry-cleaning. In dry-cleaning, clothes are not washed with water; instead, an organic solvent (a liquid that can dissolve grease and oil but is itself almost non-polar) is used. These solvents lift dirt without wetting the fabric with water. Commonly employed dry-cleaning solvents in the chemical industry include chlorinated hydrocarbons and, more recently, super-critical or liquid $$\mathrm{CO_2}$$ because of its low environmental impact.

Let us now look at every option one by one and match it with the list of known dry-cleaning agents.

First option: $$\mathrm{H_2O_2}$$ is hydrogen peroxide. It is widely recognised as an oxidising and bleaching agent. It liberates nascent oxygen according to the reaction $$\mathrm{H_2O_2 \;\rightarrow\; H_2O + \tfrac12\,O_2\uparrow}$$ and therefore is mainly used for bleaching hair, paper pulp, cotton etc. Because it is an aqueous solution and works by oxidation in water, it is not suitable for the non-aqueous process called dry-cleaning.

Second option: $$\mathrm{CCl_4}$$ is carbon tetrachloride. This compound is a non-polar liquid, so it dissolves greasy dirt and has historically been used as a dry-cleaning solvent (although now phased out for toxicity reasons). Hence it is a recognised dry-cleaning agent.

Third option: liquid $$\mathrm{CO_2}$$. Under high pressure, carbon dioxide can exist as a liquid or super-critical fluid. Super-critical $$\mathrm{CO_2}$$ has become a modern, eco-friendly alternative to chlorinated solvents in dry-cleaning. Therefore liquid $$\mathrm{CO_2}$$ also fits the definition of a dry-cleaning agent.

Fourth option: $$\mathrm{Cl_2C{=}CCl_2}$$ is perchloroethylene (also called tetrachloroethylene). Its non-polarity and high density make it the most widely used commercial dry-cleaning solvent. Thus it clearly belongs to the family of dry-cleaning agents.

From the discussion above, the only substance that does not qualify as a dry-cleaning solvent is hydrogen peroxide, $$\mathrm{H_2O_2}$$, which is actually a water-based bleach.

Hence, the correct answer is Option A.