The minimum investment in stocks depends on the stock price. The minimum investment will be equivalent to the market price of 1 share of the company you want to buy. To diversify across Nifty 50 companies, you will need more than Rs. 1 lakh to buy just one share of each of the Nifty 50 companies.
In the case of mutual funds, the minimum investment usually starts from Rs. 100. To diversify across the Nifty 50 companies, you will need just Rs. 100 to invest in a Nifty 50 Index fund.