Paheli and Boojho observe a bright object in the night sky which was not twinkling. Paheli says, it is a star and Boojho says it is a planet. Who is correct?

Boojho is correct. Planets do not twinkle. The twinkling of stars is because of the phenomenon of apparent objects. If we observe a small object placed far away from our eyes, it will appear to be twinkling. But planets being bigger in size as they are nearer to our planet as opposed to stars, the twinkling effect does not occur.