In the reaction sequence $A$ $\xrightarrow{K_1} B$ $\xrightarrow{K_2} C$ $\xrightarrow{K_3} D$,where $K_3 > K_2 > K_1$,which step determines the rate of the reaction?

Consider the following single step reaction in gas phase at constant temperature.
$2 \ A_{(g)} + B_{(g)} \rightarrow C_{(g)}$
The initial rate of the reaction is recorded as $r_1$ when the reaction starts with $1.5 \ atm$ pressure of $A$ and $0.7 \ atm$ pressure of $B$. After some time,the rate $r_2$ is recorded when the pressure of $C$ becomes $0.5 \ atm$. The ratio $r_1 : r_2$ is $\qquad$ $\times 10^{-1}$.
(Nearest integer)

For $n$th order of reaction,half-life period is directly proportional to

What is the order of a reaction which has a rate expression $\text{rate} = K[A]^{3/2}[B]^{-1}$?

........ of a reaction cannot be determined experimentally.

The rate constant for the reaction,$2N_2O_5 \to 4NO_2 + O_2$ is $3 \times 10^{-5} \, s^{-1}$. If the rate is $2.40 \times 10^{-5} \, mol \, L^{-1} \, s^{-1}$,then the concentration of $N_2O_5$ (in $mol \, L^{-1}$) is