If the half-life of a reaction is halved when the initial concentration of the reactant is doubled,what is the order of the reaction?

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)

For a second-order reaction where the initial concentrations of both reactants are equal,it takes $3000 \ s$ for the reaction to be $60\%$ complete. How much time (in $s$) will it take for the reaction to be $20\%$ complete?

The rate of reaction,$A + B + C \longrightarrow P$ is given by
$r = K[A]^{1/2} [B]^{1/2} [C]^{1/4}$
The order of reaction is

Write the differential rate expression for the following reactions and determine their order of reaction:
$1) \ 2 N_2O_5(g) \rightarrow 4 NO_2(g) + O_2(g)$
$2) \ C_4H_9Cl(aq) + OH^-(aq) \rightarrow C_4H_9OH(aq) + Cl^-(aq)$

Rate law for the reaction $aA + bB \rightarrow cC + dD$ is $r = k[A][B]$. Which of the following conditions does $NOT$ affect the rate of reaction?