Which of the following is an elementary reaction?

Rate constant of a reaction, $$ 2 \mathrm{NO}_2 \mathrm{Cl}_{2(\mathrm{~g})} \longrightarrow 2 \mathrm{NO}_{2(\mathrm{~g})}+\mathrm{Cl}_{2(\mathrm{~g})}$$

is 4.7672 minute $^{-1}$. Calculate half life of reaction.

Initial concentration of reactant in a first order reaction is $0.08 \mathrm{~mol} \mathrm{~dm}^{-3}$ What concentration would remain after 40 minute?

$$\left(\text { given } \frac{[\mathrm{A}]_0}{[\mathrm{~A}]_{\mathrm{t}}}=5.00\right)$$

For the reaction $\mathrm{A}+\mathrm{B} \longrightarrow$ product, rate law equation is, rate $=k[A]^2[B]$. If rate of reaction is $0.22 \mathrm{~mol} \mathrm{~L}^{-1} \mathrm{~s}^{-1}$, calculate rate constant. ($\mathrm{[A}]=1 \mathrm{~mol} \mathrm{~L}^{-1},[\mathrm{~B}]=0.25 \mathrm{~mol} \mathrm{~L}^{-1})$