b
$20 \; MSD =1 \; cm$
$1 \; MSD =\frac{1}{20} \; cm$
$10 \; VSD =9 \; MSD$
$1 \; VSD =\frac{9}{10} \; MSD$
$=\frac{9}{10} \times \frac{1}{20} \; cm$
$1 VSD =\frac{9}{200} \; cm$
VC $=1 MSD -1 \; VSD$
$=\frac{1}{20} \; cm -\frac{9}{200} \; cm$
$=\frac{1}{200} \times 10 \; mm$
VC $=5 \times 10^{-2} \; mm$
Ans. $5$