The correct answer is: Only 2.
Benzene, carbon tetrachloride, and sodium carbonate are not used as dry cleaning chemicals. Benzene is a highly flammable and toxic chemical that is no longer used in dry cleaning. Carbon tetrachloride is also a highly flammable and toxic chemical that is no longer used in dry cleaning because it is a known carcinogen. Sodium carbonate is a common household chemical that is used for a variety of purposes, but it is not used in dry cleaning.
Trichloroethylene is a common dry cleaning solvent. It is a colorless, nonflammable liquid that is effective at removing grease and oil from fabrics. However, trichloroethylene is a known carcinogen and is no longer used in many countries.
In recent years, there has been a trend towards using more environmentally friendly dry cleaning solvents, such as carbon dioxide and hydrocarbon solvents. These solvents are less toxic than trichloroethylene and do not pose the same health risks.