Please tel me natural ways of increasing body weight.........

Muscle over fat: At 16 yo you still have a lot of growing to do. Many guys want to "bulk up" but a better goal is to increase muscle while avoiding storing fat. Protein, good fats, and complex carbs are the micronutrients. Eat from those three groups primarily and avoid junk food or drinking lots of soda to gain fluid weight which doesn't help. Run from any temptation to take steroids; they will harm you.