An ideal air$-$filled parallel$-$plate capacitor has round plates and carries a fixed amount of equal but opposite charge on its plates. All the geometric parameters of the capacitor $($plate diameter and plate separation$)$ are now DOUBLED. If the original capacitance was $C_0,$ what is the new capacitance?

$4C_0$

$\frac{C_0}{4}$

$2C_0$

$\frac{C_0}{2}$

$c_0$