Chlorine gas was used earlier for bleaching paper. These days, hydrogen peroxide ( $\mathrm{H}_2 \mathrm{O}_2$ ) with suitable catalyst. Tetra chlroroethene $\left(\mathrm{Cl}_2 \mathrm{C}=\mathrm{CCl}_2\right)$ was earlier used as solvent for dry cleaning. The compound contaminates the ground water and is also a suspected carcinogen. Replacement of halogenated solvent by liquid $\mathrm{CO}_2$ will result in less harm to groundwater. Hence given statement $(4)$ is correct.