Capital gain exemption u/s 54f

No,problem.Sec54F was inserted by Government to encourage House hold sector.They will see whether you invested in Residential property or not but not bother about whether you purchased the property in assessee name or as a joint property to give you capital gain exemption.This is just my opinion,i too need a furthur clarification

As such there is no problem in no problem in joint ownership, there are several HC judgements

(In one it was husband and wife CIT v. Ravinder Kumar Arora 342 ITR 38,  and I have quoted few more in my earlier posts)

 But payment made by the son would be a problem, since payment should have been made by the assesse only, though she could use whatever source of funds she wanted. So there will be a proportionate disallowance, to the extent sum not paid by assessee herself 

Agree with "Z",Yes payment for such transaction should be made by the assessee him/herself !