4. d and f- block elements — Chemistry STD 12 Science — Question

$H{_2(g)} + 2ICl_{(g)} \to 2HCl_{(g)} + I_{2(g)}$

This reaction is of first order with respect to $H_{2(g)}$ and $ICl_{(g)}$ , following mechanisms were proposed

Mechanism $A$ :

$H{_2(g)} + 2ICl_{(g)} \to 2HCl_{(g)} + I_{2(g)}$

Mechanism $B$ :

$H_{2(g)} + ICl_{(g)} \to HCl_{(g)} + HI_{(g)}$  ;   Slow

$HI_{(g)} + ICl_{(g)} \to HCl_{(g)} + I_{2(g)}$  ;  Fast

Which of the above mechanism $(s)$ can be consistent with the given information about the reaction