A graph between ${\mathrm{t}}_{1/2}$ and concentration for ${\mathrm{n}}^{\mathrm{th} }$ order reaction is a straight line. Reaction of this nature is completed $50\%$ in $10$minutes when concentration is $2 \mathrm{mol} {\mathrm{L}}^{-1}$. This is decomposed $50\%$ in $\mathrm{t}$ minutes at $4$$\mathrm{mol}$ ${\mathrm{L}}^{-1}, \mathrm{n}$ and $\mathrm{t}$ are respectively

The reaction 

$2{\mathrm{N}}_2{\mathrm{O}}_5\left(\mathrm{g}\right)\to 4{\mathrm{NO}}_2\left(\mathrm{g}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right)$

is first order with respect to ${\mathrm{N}}_2{\mathrm{O}}_5$ Which of the following graph would yield a straight line :-

The following data were obtained at a certain temperature for the decomposition of ammonia

$$\begin{gathered} \mathrm{p} \left(\mathrm{mm}\right) 50 100 200 \\ {\mathrm{t}}_{1/2 3.64 1.82 0.91 } \end{gathered}$$
The order of the reaction is :-