If the field is vertical then it will affect the SHM. We have to see whether the force qE (where q is the charge and E is the electric field) is dowdward or upward. If the time period is T=2∏√(l/g) then it will be
g′=g+qE/m when force is downward
g′=g-Eq/m when force is upward.
So in your case the force is upward therefore, its time period will increase.
option (A) is correct