When a convex lens of glass is immersed in water, its power will

decrease

The correct answer is Option (2) → decrease

Power of a lens is given by:

$P = \left(\frac{n_{lens}}{n_{medium}} - 1\right)\left(\frac{1}{R_1} - \frac{1}{R_2}\right)$

When the lens is in air: $n_{medium} = 1$

When immersed in water: $n_{medium} = 1.33$

Since $\frac{n_{lens}}{n_{medium}} - 1$ decreases in water, the effective power decreases.

Correct option: decrease