d
(d) They will not experience any force if \(|\overrightarrow {{F_G}} |\, = \,|\overrightarrow {{F_e}} |\)
\(==>\) \(G\frac{{{m^2}}}{{{{(16 \times {{10}^{ - 2}})}^2}}} = \frac{1}{{4\pi {\varepsilon _0}}}.\frac{{{q^2}}}{{{{(16 \times {{10}^{ - 2}})}^2}}}\) \(==>\) \(\frac{q}{m} = \sqrt {4\pi {\varepsilon _0}G} \)