One problem of a reflecting telescope is that its

The correct answer is Option (1) → Objective mirror focuses light inside the telescope tube.

In a reflecting telescope the concave objective mirror brings the light to a focus inside the telescope tube, in the path of the incoming light. An eyepiece and observer placed there would block part of the light, so a secondary mirror is used to send the light out of the tube, as in the Cassegrain telescope.

NCERT (2026-27):
Telescope – “… Telescopes with mirror objectives are called reflecting telescopes. … One obvious problem with a reflecting telescope is that the objective mirror focusses light inside the telescope tube. One must have an eyepiece and the observer right there, obstructing some light (depending on the size of the observer cage).”