If the focal length of an objective lens is decreased, then the magnifying power of:

the microscope will increase but that of the telescope will decrease

The correct answer is Option (1) → the microscope will increase but that of the telescope will decrease

The magnifying power of a compound microscope is -

$M=\left(\frac{v_0}{f_0}\right)\left(1+\frac{D}{f_e}\right) [$f_0$ focal length of objective lens]

$⇒M∝\frac{1}{f_0}$

∴ Magnifying power of a focal length will increase as focal length of objective lens is decreased.

and,

Magnifying power of a telescope, $M=\frac{f_0}{f_e}$

$⇒M∝f_0$

∴ Magnifying power of Telescope will decrease as focal length of objective lens is decreased.