b
$50 VSD =2.45 \ cm $
$1 VSD =\frac{2.45}{50} cm =0.049 \ cm $
$\text { Least count of vernier }=1 MSD -1 VSD $
$=0.05 cm -0.049 \ cm $
$=0.001 \ cm $
$\text { Thickness of the object }=\text { Main scale reading }+ \text { vernier scale reading } \times \text { least count } $
$=5.10+(24)(0.001) $
$=5.124 \ cm .$