I am 24 yrs old and my weight is 50kgs and height 168cms. Can you please suggest me the food to gain weight.

You could try sweets, like cookies and cakes. Or you could eat chips, not Sun Chips. Just about anything you eat, if you eat enough of it, can make you gain weight. Too much food will make you gain weight, but look for things with high fats content. They tend to work best.