Question

cheque paid to mr das for rs 25 was posted to the wrong side of his account rectify

Answer 1

As the question quotes word paid so hereby assumed that Mr das is creditor.
And the entry will be

Mr Das A/c Dr
To cash/ bank a/c
( being entry rectified)
The amount should be twice the amount posted is wrong entry.
Suppose the wrong entry was of 20 rs
The rectification entry should be of 40 rs.
Hopw this helps