A bubble in glass slab (µ = 1.5) when viewed from one side appears at 5 cm and 2 cm from otherside, then the thickness of the glass slab is:

2.5 cm 7.5 cm 10.5 cm 17.5 cm

10.5 cm

Real depth = $\mu$ \times apparent depth  $ \text{Real depth} = 1.5\times (5+2) cm = 10.5 cm$