Answer
(a) Electrons have been removed from the rod and transferred to the sphere.
(b) $3.1\times 10^{10}$ electrons were transferred.
Work Step by Step
(a) Since it is normally quite easy for electrons to move, we can assume that it is the electrons which are transferred when there is a transfer of charge. The charge on the rod changes by +5.0 nC, so a charge of -5.0 nC was removed from the rod. In this case, we can assume that electrons have been removed from the rod and transferred to the sphere.
(b) A total charge of $-5.0~nC$ was removed from the rod. Each electron has a charge of $-1.6\times 10^{-19}~C$. We can find the number of electrons that were transferred.
$\frac{-5.0\times 10^{-9}~C}{-1.6\times 10^{-19}~C} = 3.1\times 10^{10}~electrons$
$3.1\times 10^{10}$ electrons were transferred.
