As per Newton's II law we know that
here
F = applied unbalanced force
m = mass of object
a = acceleration of object
now it is given that force F = 50 N North applied on block on earth due to which block will accelerate by 4 m/s^2
so here from above equation
Now we took another situation where block is placed on surface of moon and again force F = 25 N is applied on the block
So we will again use Newton's II law
so block will accelerate on moon by acceleration 2 m/s^2