From the supply of identical capacitors rated 8 mF, 250volt, The minimum number of capacitors required to form a composite 16 mF, 1000 v  capacitor is 

The combination of capacitors should be as shown in the figure,

$\begin{array}{l}{\mathrm{C}}_{\mathrm{E}}=\frac{\mathrm{c}}{4}\times 8=2\mathrm{c}=2\times 8\mathrm{mF}\\ {\mathrm{C}}_{\mathrm{E}}=16\mathrm{mF}\\ \mathrm{Also}{\mathrm{V}}_{\mathrm{A}}-{\mathrm{V}}_{\mathrm{B}}=4\times 250\mathrm{v}\\ =1000\mathrm{volt}\end{array}$

Hence total number of capacitors required$=8\times 4=32$