What is the effect on the focal length of a convex lens when it is immersed in a liquid whose refractive index is equal to refractive index of the lens?

Focal length will become infinity Focal length will become zero Focal length will reduce but not become zero Focal length remains unchanged

Focal length will become infinity

$\frac{1}{f} = (\frac{\mu_2}{\mu_1} - 1)(\frac{1}{R_2} - \frac{1}{R_1})$ Here $\mu_2 =\mu_1$ $\Rightarrow \frac{1}{f} = 0$ $f \rightarrow \infty$ A convex lens is dipped in a liquid whose refractive index is equal to the refractive index of the lens. Then its focal length will. become infinite.