If someone has 60 lakh rupees to invest, in what ways should he invest risk free or a minimum possible risk to generate a fixed income of 1 lakh rupees per month?

The 20% return you are aiming is very aggressive. If you are interested in an income stream, and are willing to stay invested for the long run, then go for a long term diversified equity mutual fund (large cap or multicap). Invest only in direct plans, otherwise you will lose 40% over long term to the distributor or app.

You can then go for a Systematic Withdrawal Plan that taps the fund for monthly income. You may not get a 20% return but in the circumstances this could be the most efficient way to realise income.