Debenture investments

Yes, it is risk averse investment with returns lower than speculation. Try mutual funds based on returns.  

But I have heard that the returns are kind of stable in debentures and if one wants security one must invest in debentures

Yes it’s true, minimum risk. Mutual funds are subject to market risks. A guy offered me a package irredeemable one and annuities for 8 years gives more returns. However, your correct, I did not try it and hence can’t preach it. Check out with your friends if their mutual funds had gone through successfully. After all, the returns are more than debentures. 

yes debentures at least have a fixed return of return in all cases. Mutual funds have higher returns but more risk. However even mutual funds are not that risky according to my opinion.