Answer:(a)does not change
Step-by-step explanation:
Given
Submarine is 50 m below the surface
Now submarine descends to 100 m and stops
As we know that pressure difference at a depth of h is given by

where
=Density of fluid
g=acceleration due to gravity
h=height below free surface of liquid
buoyant force is equal to volume displaced by object
as the submarine is already in water therefore buoyant force will remain same.