Explanation: The time constant (τ) in an RC circuit is a critical value determined by multiplying the resistance (R) by the capacitance (C). It represents the time it takes for a capacitor to charge or discharge a specific amount exponentially. When charging, the capacitor voltage increases over time: * After one time constant (1τ), the capacitor charges to approximately 63.2% of the supply voltage. * After two time constants (2τ), it charges further to approximately 86.5% of the supply voltage. * After three time constants (3τ), it reaches about 95% of the supply voltage. * By five time constants (5τ), it's considered fully charged (over 99%). Therefore, after two time constants, the capacitor is charged to 86.5% of the supply voltage. * A) 36.8% represents the remaining voltage after one time constant of discharge, not charge. * B) 63.2% is the charge after one time constant. * D) 95% is the charge after three time constants.