Dear Anjali,
Don’t worry as your age is 16 years and your weight is 41kg. Actually it’s depend on you height. if your height is above 5feet then your waight shouldn't be more then 48 kg. so u can decide accordingly and moreover you are at your teen age you need to take 3 meals at least a day. i'll give you one suggestion kindly take frequent meal which will help you to gain weight. Do take milk, boil eggs (if you are non-vegetarian), green salad, bananas and protein and calcium food. Don’t try any medicines to gain wait.
Regards
Nancy