Please answer the following questions and also mention the concepts involved and why the incorrect options are wrong.

Dear student,

Potential energy change dU= q dV

=- q E.dr

In one dimensional case dU = - qE dy .In your problem  E is taken  along + ve y direction . Then potential decreases in reverse direction . So take E =+ 50 V/m . y decreasing and so dy is - ve.q is -ve and so -q E dy is +ve and so dU is +ve i.e, U increases.

Regards