Income tax to be paid by different person other than assesee

hi everybody

kindly help me out.

i am selling a immovable property to a person A. now A is paying the entire money by way of cheque. he has also agreed to pay whatever income tax liability that i shall be subject to he shall be paying it. this shall be by way of a separate contract, in which he shall be giving me a pdc for the amount that i shall be paying as income tax.

now i want to know:

1) what is the legal validity of such a contract?

2) what is the legality of the cheque and what about the applicability of sec 138 of NI act if the cheque bounces?

thanks in advance