Quantization of Electric Charge

Steps:

• Electric charge is quantized: q = n e, where e = 1.6 × 10^{-19} C and n is an integer (Millikan's oil drop experiment).
• Compute n for each option by dividing q by e.
• A: -4.8 × 10^{-19} / 1.6 × 10^{-19} = -3 (integer).
• B: -3.2 × 10^{-19} / 1.6 × 10^{-19} = -2 (integer); C: -2.4 × 10^{-19} / 1.6 × 10^{-19} = -1.5 (non-integer); D: 3.2 × 10^{-19} / 1.6 × 10^{-19} = +2 (integer).

Why C is correct:

• Charge must be an integer multiple of e per quantization law; -2.4 × 10^{-19} C equals -1.5 e, violating this.

Why the others are wrong:

• A: Equals -3e, possible for three electrons.
• B: Equals -2e, possible for two electrons.
• D: Equals +2e, possible for two protons.

Final answer: C