Answer : 3. "20 जुलाई "
Explanation :

1. Every year 20th July is celebrated as World Chess Day all over the world.

2. The game of chess is a very peaceful but entertaining game, which requires a lot of brain power, hence it is also called mind game.

3. 20th July was chosen as Chess Day because the International Chess Federation was established in Paris in 1924 on 20th July.