b
સંતુલન માટે $QE = Mg ⇒ (Ne)E = Mg$
$N\,\, = \,\,\frac{{Mg}}{{eE}}\,\,\,\left\{ {\left. {E\,\, = \,\,\frac{V}{d}} \right\}} \right.\,\,$
$ = \,\,\frac{{1.96\,\, \times \,\,{{10}^{ - 15}}\, \times \,\,10\,}}{{1.6\,\, \times \,\,{{10}^{ - 19}}\,\, \times \,\,\left( {800/0.02} \right)}}\,\, = \,\,3\,$
$\,\therefore \,\,Q\,\, = \,\,Ne\,\, = \,\,3e$