# How is PVC made soft?

$\begin{array}{1 1}(a)\;\text{By adding HCl}\\(b)\; \text{By adding }CH_3COOH\\(c)\;\text{ By adding di-n-heptyl phphalate}\\(d)\;\text{By adding di-n-butyl phphalate}\end{array}$

Polyvinyl chloride (PVC) is very stiff and hard but it is made soft by adding di-n-butyl phthalate(a plasticizer)
Hence (d) is the correct answer.