The reaction of hydrogen and iodine monochloride is given as:${\text{H}}_2(g)+2\text{ICl}(g)\to 2\text{HCl}(g)+{\text{I}}_2(g)$ This reaction is of first order with respect to ${\text{H}}_2(g)$ and $\text{ICl}(g)$. The following mechanisms were proposed:Mechanism A: ${\text{H}}_2(g)+2\text{ICl}(g)\to 2\text{HCl}(g)+{\text{I}}_2(g)$ Mechanism B:${\text{H}}_2(g)+\text{ICl}(g)\to \text{HCl}(g)+\text{HI}(g)$ (slow)$\text{HI}(g)+\text{ICl}(g)\to \text{HCl}(g)+{\text{I}}_2(g)$ (fast)Which mechanism is consistent with the rate law?

1. A
   B Only
2. B
   A and B both
3. C
   Neither A nor B
4. D
   A only