The increasing order of reduction of alkyl halides with zinc and dilute HCl is
1. R−Cl<R−I<R−Br
2. R−Cl<R−Br<R−I
3. R−I<R−Br<R−Cl
4. R−Br<R−I<R−Cl
HINT: Weaker bond of halogen with carbon gets easily reduced.
EXPLANATION (2).
The reactivity of halogens with alkane is F2>Cl2>Br2>I2. Hence, reduction of alkyl halide with Zn and dilute HCl follows reverse order i.e., R−I>R−Br>R−Cl. Further, the reactivity of this reduction increases as the strength of C-X bond decreases.