In the circuit element given here, if the potential at point B, i.e, VB = 0, then the potentials of A and D ate given as

Potential difference between A and B,VA −VB=1 ×1.5 ⇒   VA −0=1.5V  ⇒  VA =1.5VPotential difference between B and C,VB −VC=1 ×2.5=2.5 V  ⇒   VC=−2.5VVC-VD=2V -2.5 -VD=-2V VD=-0.5V