The tension in the string connected between blocks is

It is given in the question that,

m1=2kg, m2= 4kg, f1=20 N and f2=10N

T is the tension between blocks.

F1> F2

We can see that the net force will act in the right direction.

For the block m2,T-F2=2a=T-10………(1)

For the block m1,20-T=4a………..(2)

By solving, we get,10=6aa=53m/s2

From (1),T=10+103=403N

Hence, the correct option is B: 403N