Charge Quantization in Charge Carriers Steps:

• Recall that the charge of any charge carrier must be an integer multiple of the elementary charge $e = 1.6 \times 10^{-19}$ C, per the law of charge quantization.
• Compute the multiple for each option by dividing the magnitude of the charge by $e$.
• For A: $4 \times 10^{-19} / 1.6 \times 10^{-19} = 2.5$ (not an integer).
• For B, C, D: 15, 10, 2 (all integers, so possible for ions or composite carriers).

Why A is correct:

• It violates charge quantization, as 2.5$e$ is not an integer multiple of $e$.

Why the others are wrong:

• B: Equivalent to -15$e$, possible for highly charged ions.
• C: Equivalent to +10$e$, possible for multiply charged ions.
• D: Equivalent to +2$e$, possible for divalent ions like Ca$^{2+}$.

Final answer: A