Which is the unit of the rate constant for a second-order reaction?

$A$ student has studied the decomposition of a gas $AB_3$ at $25^{\circ} C$. He obtained the following data.

$p \ (mm \ Hg)$	$50$	$100$	$200$	$400$
Relative $t_{1/2} \ (s)$	$4$	$2$	$1$	$0.5$

The order of the reaction is

For the reaction $Cl_{2(aq)} + H_2S_{(aq)} \to S_{(s)} + 2H^{+}_{(aq)} + 2Cl^{-}_{(aq)}$,the rate law is $r = K[Cl_2][H_2S]$. Which of the following mechanisms is/are consistent with this rate law?
$A. \ H_2S \rightleftharpoons H^{+} + HS^{-}$ (fast)
$Cl_2 + HS^{-} \to 2Cl^{-} + H^{+} + S$ (slow)
$B. \ Cl_2 + H_2S \to H^{+} + Cl^{-} + Cl^{+} + HS^{-}$ (slow)
$Cl^{+} + HS^{-} \to H^{+} + Cl^{-} + S$ (fast)

For a reaction $A \rightarrow \text{Product}$,the rate constant is $6.93 \times 10^{-3} \ hour^{-1}$. What is the order of the reaction?

Find the rate law for the reaction,$CHCl_{3(g)} + Cl_{2(g)} \rightarrow CCl_{4(g)} + HCl_{(g)}$ if the order of reaction with respect to $CHCl_{3(g)}$ is $1$ and with respect to $Cl_{2(g)}$ is $1/2$.

Rate of reaction for $2X + Y \rightarrow 3W + Z$ is $1.2 \times 10^{-4} \ mol \ dm^{-3} \ sec^{-1}$ when $[X] = [Y] = 0.6 \ mol \ dm^{-3}$. Calculate the value of the rate constant if the reaction is first order in $X$ and zero order in $Y$.