Correct Option
The correct option is 1.6×10−19 C.
Explanation
The elementary charge ($e$) is a fundamental physical constant representing the magnitude of electric charge carried by a single electron or proton. It is the smallest unit of charge that can exist freely in nature (excluding quarks, which are not found in isolation).
Detailed Analysis
- 1.6×10−19 C is Correct: The magnitude of the charge on an electron is approximately $1.602 \times 10^{-19}$ Coulombs (C). While an electron carries a negative charge ($-e$) and a proton carries a positive charge ($+e$), the magnitude is identical for both.
- 1.6×10−19 J is Incorrect: The value $1.6 \times 10^{-19}$ is numerically correct, but the unit provided is Joules (J). Joules are the SI unit for energy, not electric charge.
- 6×1018 C is Incorrect: The value $6 \times 10^{18}$ (specifically $6.25 \times 10^{18}$) represents the approximate number of electrons required to constitute a total charge of 1 Coulomb. It is derived from the relation $n = \frac{q}{e}$.
- 1 C is Incorrect: 1 Coulomb is a macroscopic unit of charge defined by the flow of current (1 Ampere for 1 second). It is extremely large compared to the microscopic charge of a single electron.
Key Takeaway: The elementary charge is the quantum of electric charge, with a magnitude of $e \approx 1.6 \times 10^{-19} \text{ C}$. Charge is quantized, meaning all observable charges are integral multiples of this value ($q = ne$).