The order of reactivity of the given haloalkanes towards nucleophile is :
The order of reactivity of the given haloalkanes towards nucleophile is :
$\mathrm{RI}>\mathrm{RBr}>\mathrm{RCl}$
$\mathrm{RCl}>\mathrm{RBr}>\mathrm{RI}$
$\mathrm{RBr}>\mathrm{RCl}>\mathrm{RI}$
$\mathrm{RBr}>\mathrm{RI}>\mathrm{RCl}$
Solution
For a given alkyl group, the order of reactivity is
$\frac{\mathrm{R}-\mathrm{I}>\mathrm{R}-\mathrm{Br}>\mathrm{R}-\mathrm{Cl}>\mathrm{R}-\mathrm{F}}{\text { increasing bond energy }}$
decreasing halogen reactivity.
This order depends on the carbon-halogen bond energy; the carbon-fluorine bond energy is maximum and thus fluorides are least reactive while carbon-iodine bond energy is minimum hence iodides are most reactive.