Explanation

(c) The number density ($n)$ of conduction electrons in the copper is a characteristic of the copper and is about $10^{29}$ at room temperature for both the copper rod $X$ and the thin copper wire $Y$.
Both $X\ and\ Y$ carry the same current $I$ since they are joined in series
From $I = nAvq$
Where $q$ is the electron charge of $1.6 \times 10^{- 19}$C,
$v$ is the drift velocity in the conductor and $A$ is the cross-sectional area of the conductor.
We may conclude that rod $X$ has a lower drift velocity of electrons compared to wire $Y$ since rod $X$ has a larger cross-sectional area. This is so because the electrons in $X$ collide more often with one another and with the copper ions when drifting towards the positive end. Thus, the mean time between collisions of the electrons is more in $X$ than $Y$.