In the circuit shown:

The current in the circuit I =(20−10)(7.5+0.5+1+1)                                          =1010=1ampThe potential difference across PS,VPS=7.5×1                                                               =7.5VThe potential difference across Q,R,VQR=1×1                                                                  =1VAs point G is connected to earth, hence potentials of R and S are zero.The direction of the current in the circuit is from P to S, hence point P is at higher potential.∴ Vp=7.5V Similarly,  VQ=−1V∴Hence (b), (c) and (d) are correct.