Answer:
Option C is the correct answer.
Explanation:
We have charge stored in a capacitor
Q = CV
C is the capacitance and V is the voltage.
A capacitor is connected to a 9 V battery and acquires a charge Q.
That is
Q = C x 9 = 9C
What is the charge on the capacitor if it is connected instead to an 18 V battery
That is
Q' = C x 18 = 9C x 2 = 2Q
Option C is the correct answer.