Solution: Answer is (a) 1020
Given $: I =1 A , t =16 s , e =1.6 \times 10^{-19} C$
Step 1: The filament draws current from the power supply.
$I =\frac{ Q }{ t }=\frac{ Ne }{ t } \quad
($ Since $Q = Ne$, where $N$ is the number of electrons crossing in time t)
$$
\Rightarrow N =\frac{ It }{ e }
$$
Step 2: Substituting the values in equation (1)
$$
N =\frac{ It }{ e }=\frac{1 A \times 16 s }{1.6 \times 10^{-19} C }=10^{20}
$$
As a result, the number of electrons passing through a cross section of the filament in 16 seconds is $10^{20}$.