From past 8 years I give money in form of cash to my mother and I am increasing the amount depending upon my salray. I was in assumption that my mother used to spent that money however recently I got to know that she saved that money and till date she saved some lakhs. I am planning to open a bank account for her to move that money int o bank and then from there move that money to Post Office Monthly scheme or Senior Citizen savings scheme for her regualr income. My query is whether that money will be taxable or questionable when I move that money on her name into bank account. I personaly think it should not be taxable but please validate.

The cash transferred by you to your mother is totally tax-free. as you have already paid tax on such money . though the money which you are willing to transfer to  bank is not taxable, any interest earned on account of such deposit made in post office/bank is  taxable in your mothers hand.  

No question will be raised against the source of income while you are depositing money. but all you need to do is apply P.A.N. card immediately for your mother  as T.D.S  deduction on interest earned is high without a P.A.N card