If the concentration of the reactants is increased,the rate of reaction

The rate of reaction $A + B \rightarrow P$ is $4 \times 10^{-2} \text{ mol dm}^{-3} \text{ s}^{-1}$. When $[A] = 0.2 \text{ mol dm}^{-3}$ and $[B] = 0.1 \text{ mol dm}^{-3}$, what is the rate constant of the reaction, if it is first order with respect to $A$ and second order with respect to $B$?

For the following rate law,determine the unit of the rate constant: Rate $= -\frac{d[R]}{dt} = k[A]^{\frac{1}{2}}[B]^{2}$

The reaction of hydrogen and iodine monochloride is given as
$H_{2(g)} + 2ICl_{(g)} \to 2HCl_{(g)} + I_{2(g)}$
This reaction is of first order with respect to $H_{2(g)}$ and $ICl_{(g)}$. Which of the following mechanisms is consistent with the given information?
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)

The mechanism of the reaction $A + 2B \to D$ is given by:
$2B \xrightarrow{k} B_2$ [Slow]
$B_2 + A \to D$ [Fast]
The rate law expression,order with respect to $A$,order with respect to $B$,and overall order are respectively:

The unit of the rate constant for an $n^{th}$ order reaction is .....