An air bubble in a glass slab with refractive index $1.5$ (near-normal incidence) is $5 \mathrm{cm}$ deep when viewed from one surface and $3 \mathrm{cm}$ deep when viewed from the opposite face. The thickness (in $\mathrm{cm}$) of the slab is

• A

  $8$
• B

  $10$
• Correct answer
  C

  $12$
• D

  $16$

Hence, the correct answer is option: 'C'.