Question

Does a convex lens becomes less convergent when it is immersed in water?

Answer 1

Yes.

Lens maker equation

$\frac{1}{f}=\frac{\mu -{\mu }_o}{{\mu }_o}(\frac{1}{R_1}-\frac{1}{R_2})$

here $\mu$ is refractive index lens

${\mu }_o$ is refractive index of medium

Now the refractive index of water (medium) is higher than air. So it can be seen that when lens is immersed in water its focal length increases as compares to focal length when it was in air. So the lens has become less convergent.