Question

Why is India cooler in December than in july

Answer 1

December is cooler than July in India :-
 
It is just because of the tilt of Earth's axis. Many people believe that the temperature changes because the Earth is closer to the Sun in summers and farther in winters. In fact, the Earth is farthest from the Sun in July and closest to the Sun in January.
During the month of July, the Sun's rays hit the Earth at a steep angle. The daylight hours allow the Earth plenty of time to reach warm temperatures because days are longer than nights in summers as far as India is concerned.
While during the month of December, the Sun's rays hit the Earth at a shallow angle and also the longer nights in India prevent the surface from warming up.

That is why December is cooler than July in India.

Answer 2

Due to the trade winds from equator which carries the cold wind from the Arabian sea. This wind replace the hotter wind and takes its place so the weather gets cooler and with more wind in December India gets cold in this month.