Which from following decides the rate of multistep reaction?

For a zero order reaction, $\mathrm{A} \longrightarrow$ product, concentration of A decreases from $1.2 \mathrm{~mol~dm}^{-3}$ to $0.4 \mathrm{~mol~dm}^{-3}$ in 240 second. What is rate constant of the reaction?

Which of the following is NOT true about order of a reaction?

Calculate rate constant of first order reaction if concentration of reactant decreases by $90 \%$ in 30 minute?