I am 21 years old. Since past 2-3 months, there has been a considerable amount of fat deposit on my thigh (part of leg above the knee) and on my tummy. This sudden increase in weight has left me bewildered.
Please suggest some specific exercises to reduce fat around these regions primarily.
Also what is the preferred food to be taken which can help in weight loss ?

If there is considerable weight gain... you are consuming too many calories. You need to look at EVERYTHING you eat and drink, as well as how much of it.

There is no food that causes weight loss... you you have to eat less of what you are eating, and give up the high calorie items the have little nutritional value. Like Starbucks Latte's and flavored coffies that can pack one hell of a wallop calorie wize.

Where that weigth goes on is based on genetic predisposition. But a good balanced exercise program is a good idea for anyone... particularly someone wanting to lose weight.

Thanks for replying @smoothy but during these months I have not taken a lot of cals.
Could there be some kind of a hormonal imbalance that is causing the weight gain?

If your usual routine, as well as eating/exercise habits, haven't changed much, and the weight gain is sudden, as you described, then it would be a good idea to see your doctor to look into other possible causes.

As DoulaC mentions... there can be other causes... if as you mention, you've not chaged what you eat and drink... and your physical activity hasn't decreased significantly.

The Rapid part is the most telling... most gains due to metabolisn slowing down as we get older (yes at your age its already slowing down) would tend to be gradual, and changes in what you eat or drink would be something you would notice if you thought back to some point well before it started.

For most people weigh gains can be traced to eating too much and not moving enough... but for some people there actually are medical causes for a drastic and sudden change in metabolism.

Looking at some of your other threads... particularly the one where you haven't had a period in over 4 months and yet you aren't pregnant, does point towards Hormone issues a doctor could test for.