For A: as battery is connected to the capacitor so potential V remains constant. When dielectric slab is removed from the capacitor, capacitance C′=kC becomes C and energy U=1/2kCV2 becomes 1/2CV2. Thus capacitance and store energy decreases. As charge Q=CV so charge on the plates decreases. so,A→4
For B: here also potential V remains constant. When dielectric slab is inserted into the capacitor, capacitance C becomes kC and energy U=1/2CV2 becomes 1/2kCV2. Thus capacitance and store energy increases. As charge Q=CV so charge on the plates increases. so B→2,3
For C: as no cell is connected to capacitor so charge remains constant. When dielectric slab is removed from the capacitor, capacitance C′=kC becomes C and energy U=1/2(Q2/kC) becomes 1/2(Q2/C). Thus capacitance decreases and store energy increases. As potential V=Q/C so potential between the plates increases. so,C→1,3
For D: here also Q remains constant. When dielectric slab is insert into the capacitor, capacitance C becomes kC and energy U=1/2(Q2/C) becomes 1/2(Q2/kC). Thus capacitance increases and store energy decreases. As potential V=Q/C so potential between the plates decreases. so,D→2