Choose the correct option to fill in the blank : He ............ sleep after reading at least 20 pages every night, when he lived in hostel.

Right Answer: would

The clause 'when he lived in hostel' fixes the action firmly in the past, and the sentence describes something he did repeatedly every night. To express a habitual or repeated action in the past, English uses the modal 'would' or the structure 'used to'. Therefore 'He would sleep after reading at least twenty pages every night' is correct. 'Will' and 'shall' refer to future time and cannot follow a past context, while 'might' expresses possibility rather than habit. Hence the correct answer is 'would'.