The correct option is A The charge crossing in a given time interval.
Since,
Charge entering at one end of a conductor = charge leaving at the other end,
So current does not change with change in cross-section and conductor remains uncharged when current flows through it.
As the cross-sections are in series, so the current in them will be the same.
From current and drift velocity relation,
I=neAvd
Since, in this case current and n are constant
∴vd∝1/A.
At one cross-section is more, hence the drift velocity is less.
And current density J is given by
J=IA
⇒J∝1A (∵I=constant)
So, current density depends upon area of cross-section.
Hence, option (a) is correct