The correct answer is
(3) 3.2 × 10^−19 C
In fact, electric charge is quantized: the elementary charge is the charge of the electron, [tex]e=1.6 \cdot 10^{-19} C[/tex], and every particle can only have an electric charge which is an integer multiple of this value. Of the options listed above, only option (3) is an integer multiple of the elementary charge: in fact, it corresponds to 2 times the electron charge:
[tex]2e=2 \cdot 1.6 \cdot 10^{-19} C=3.2 \cdot 10^{-19} C[/tex]
