If you invest Rs 1,50,000 each year in PPF for the next 15 years. And if it offers interest at the rate of 7.1% throughout 15 years (which may not be the case in the future though) the accumulated amount would be Rs 40,68,209. (where the invested amount is Rs 22,50,000 and interest earned is Rs 18,18,209 which will be totally tax-free as per current prevailing income tax law)

Whereas If you invest Rs 12,500 each month (1,50,000 each year) in equity mutual funds for the next 15 years. And if it offers to return at the rate of 11% throughout 15 years (return earned in equity mutual funds may not be linear each year, it fluctuates but, in the long run, it may offer less/more return than mentioned). the accumulated amount would be Rs 57,35,720. (where the invested amount is Rs 22,50,000 and return earned is Rs 34,85,720which will be taxed at the rate of 10% after 1 lac profit as per current prevailing income tax law).

If one invests 50:50 in both these instruments the PPF will fetch: Rs 20,34,105

and mutual fund investment will fetch around: Rs 28,67,860

So if you have a combination of these 2 products for your retirement planning as per your risk-taking ability then your risk is also managed and you let some of your investment earn the inflation hedged return.