Two circle $S_1=p x^2+p y^2+2 g^{\prime} x+2 f^{\prime} y+d=0$ and $S_2=x^2+y^2+2 g x+2 f y+d^{\prime}=0$ have a common chord $P Q$. The equation of $\mathrm{PQ}$ is

• A

  $S_1-S_2=0$
• B

  $S_1+S_2=0$
• Correct answer
  C

  $\mathrm{S}_1-\mathrm{pS}_2=0$
• D

  $\mathrm{S}_1+\mathrm{pS}_2=0$

Hence, the correct answer is option: 'C'.