The ratio of the focal lengths of a convex lens when kept in air and when it is immersed in a liquid is $1: 2$. If the refractive index of the material of the lens is 1.5, then the refractive index of the liquid is

• Correct answer
  A

  $1.20$
• B

  $1.30$
• C

  $1.25$
• D

  $1.35$

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