A backup power system uses a 25 μF25\ \mu\text{F}25 μF capacitor to keep a memory chip active during a power glitch. When the power fails, the capacitor discharges through a resistor of resistance 120 kΩ120\text{ k}\Omega120 kΩ. What fraction of the capacitor's original charge remains after 4.5 s?
0.350.350.35
0.220.220.22
0.510.510.51
0.780.780.78
