The correct option is B 0.4 N
If there is no change in volume of cell then it means that the solution is isotonic i.e., of same concentration to cell sap.
Normality (N) = n X M
where, 'n' is the 'n-factor'
Since common salt has n-factor of 1, N=M
Hence, the concentration of the cell sap is 0.4 N.