The velocity of light in diamond, glass and water decreases in the following order:

Water > glass > diamond

The correct answer is Option (1) → Water > glass > diamond

V, velocity of light in a medium is inversely proportional to the refractive index, u.

$v=\frac{c}{u}⇒v∝\frac{1}{u}$

$u_{Diamond}>u_{Glass}>u_{Water}$

$∴ v_{Diamond}<v_{Glass}<v_{Water}$