Simple Pendulum question from JEE Main 2022 (29 Jul, Shift 1)

Answer: (a)

1. The vehicle slides freely with acceleration $g\sin\alpha$ down the incline.
2. In its frame the pseudo force cancels the along-incline part of gravity, leaving $g_{eff} = g\cos\alpha$ (perpendicular to the incline).
3. So the answer is (a) $2\pi\sqrt{L/(g\cos\alpha)}$.