Where shall I invest a lump sum of 1 lac for 20 years to earn a decent amount of profit?

Investing for the long run is a good idea. And over 20 years, your investment can multiply upto 8 times assuming decent return of 11% to 12%.

Go for 2 or 3 equity mutual funds that invest in large cap or multicap companies. Over time you will accumulate considerable wealth. Suggested funds for the long term can be found here.

However be sure to invest only in direct plans of mutual funds otherwise you will end up gifting away 40% of your entire investment to the broker or app that gives you ‘regular plans’ (i.e. one which is not a ‘direct plan’).