The reaction of hydrogen and iodine monochloride is given as :
$H_{2(g)} + 2ICl_{(g)} \rightarrow 2HCl_{(g)} + I_{2(g)}$
This reaction is of first order with respect to $H_{2(g)}$ and $ICl_{(g)}$. The following mechanisms were proposed:
Mechanism $A$ :
$H_{2(g)} + 2ICl_{(g)} \rightarrow 2HCl_{(g)} + I_{2(g)}$
Mechanism $B$ :
$H_{2(g)} + ICl_{(g)} \rightarrow HCl_{(g)} + HI_{(g)}$ ; (slow)
$HI_{(g)} + ICl_{(g)} \rightarrow HCl_{(g)} + I_{2(g)}$ ; (fast)
Which of the above mechanism$(s)$ can be consistent with the given information about the reaction?

• A
  $A$ and $B$ both
• B
  Neither $A$ nor $B$
• C
  $A$ only
• D
  $B$ only