What is the order of reaction for the decomposition of gaseous acetaldehyde?

In the reaction $2A + B \to A_2B$,if the concentration of $A$ is doubled and the concentration of $B$ is halved,then the rate of the reaction will:

For the reaction $2 NO_{(g)} + Cl_{2_{(g)}} \rightarrow 2NOCl_{(g)}$,when the concentration of $Cl_2$ is doubled,the rate of the reaction becomes twice the original rate. When the concentration of $NO$ is doubled,the rate becomes four times the original rate. What is the overall order of the reaction?

The half-life periods of decomposition of $PH_3$ for different initial pressures are given below $:$

Initial Pressure $p$ (torr)	$707$	$79$	$37.5$
Half-life $t_{1/2}$ (min)	$84$	$84$	$84$

Determine the order of the reaction.

The mechanism for the reaction is given below:
$2P + Q \to S + T$
$P + Q \to R + S$ (slow)
$P + R \to T$ (fast)
The rate law expression for the reaction is:

Assertion : In rate law,unlike in the expression for equilibrium constants,the exponents for concentrations do not necessarily match the stoichiometric coefficients.
Reason : It is the mechanism and not the balanced chemical equation for the overall change that governs the reaction rate.