Rate law for the reaction $aA + bB \rightarrow cC + dD$ is $r = k[A][B]$. The rate of reaction doubles if:

For a second-order reaction where both reactants have the same initial concentration,it takes $500 \ s$ for the reaction to be $20\%$ complete. How many seconds will it take for the reaction to be $80\%$ complete (in $s$)?

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?

Assuming the reaction $2NO_{(g)} + Cl_{2(g)} \longrightarrow 2NOCl_{(g)}$ occurs in a single elementary step,we can say that

If $r = k[A]^2[B]$ is the rate law equation for the reaction $A + B \rightarrow C$,at $[A] = 1 \ M$ and $[B] = 0.2 \ M$,calculate the rate of reaction if the rate constant is $6.25 \ M^{-2} \ s^{-1}$. (in $M \ s^{-1}$)

The rate constant for a reaction is $10.8 \times 10^{-5} \ mol \ L^{-1} \ s^{-1}$. The order of the reaction is .......