What is the molecularity of the following reaction ?

$1.$ $NH _{4} NO _{2( s )} \rightarrow N _{2( g )}+2 H _{2} O$

$2.$ $2 HI \rightarrow H _{2}+ I _{2}$

$3.$ $2 NO + O _{2} \rightarrow 2 NO _{2}$

In the reaction : $P + Q \longrightarrow  R + S$ the time taken for $75\%$ reaction of $P$ is twice the time taken for $50\%$ reaction of $P$. The concentration of $Q$ varies with reaction time as shown in the figure. The overall order of the reaction is

Diazonium salt decomposes as ${C_6}{H_5}N_2^ + C{l^ - } \to {C_6}{H_5}Cl + {N_2}$ At ${0\,^o}C$, the evolution of ${N_2}$ becomes two times faster when the initial concentration of the salt is doubled. Therefore, it is

State a condition under which a bimolecular reaction is kinetically first order reaction.

For a reaction of order $\mathrm{n}$, the unit of the rate constant is :

The half life for second order reaction is $30\, minutes$. If the initial concentration is $0.1\, M$ then the value of rate constant will be ............ $M^{-1}\, min^{-1}$