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.



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.