Introduction:
In a resistive circuit, the instantaneous voltage can be determined by the product of the resistance and the instantaneous current. This relationship is derived from Ohm's Law, which states that the voltage across a resistor is equal to the product of the current flowing through it and its resistance.

Explanation:
To understand why the instantaneous current is the correct choice for calculating the instantaneous voltage in a resistive circuit, let's briefly discuss the other options:

1. Average Current: The average current is determined by taking the average of the instantaneous current over a given time period. However, using the average current to calculate the instantaneous voltage would not accurately represent the voltage at any specific moment in time.

2. RMS Current: The Root Mean Square (RMS) current is a measure of the effective or equivalent current in an AC circuit. It is calculated by taking the square root of the average of the squares of the instantaneous current over a complete cycle. While the RMS current is useful for calculating power and determining the heating effect of the current, it does not directly represent the instantaneous current at any given moment.

3. Peak Current: The peak current is the maximum value reached by the instantaneous current in an AC circuit. While it provides information about the maximum current magnitude, it does not give insight into the instantaneous current at any other point in time.

Why is Instantaneous Current the Correct Choice?
The instantaneous current refers to the current at a specific moment in time. In a resistive circuit, the voltage across the resistor is proportional to the current flowing through it. This relationship is expressed by Ohm's Law as V = IR, where V is the voltage, I is the current, and R is the resistance.

By using the instantaneous current, we can calculate the voltage at any point in time by multiplying it with the resistance. This allows us to determine the voltage waveform across the resistor at any given moment, capturing its fluctuations and variations accurately.

Therefore, in a resistive circuit, the instantaneous voltage is a product of the resistance and the instantaneous current.