Mechanism of a hypothetical reaction,

 ${\mathrm{X}}_2+{\mathrm{Y}}_2\to 2\mathrm{XY}\mathrm{is}\mathrm{given}\mathrm{as}$

i .${\mathrm{X}}_2\rightleftharpoons \mathrm{X}+\mathrm{X}\left(\mathrm{fast}\right)$

ii.$\mathrm{X}+{\mathrm{Y}}_2\to \mathrm{XY}+\mathrm{Y}\left(\mathrm{slow}\right)$

iii.$\mathrm{X}+\mathrm{Y}\to \mathrm{XY}\left(\mathrm{fast}\right)$

False statement about order is

For equation (1)

${\mathrm{K}}_{\mathrm{eq}}=\frac{{\left[\mathrm{X}\right]}^2}{\left[{\mathrm{X}}_2\right]}$

$\left[\mathrm{X}\right]={\mathrm{K}}_{\mathrm{eq}}^{\frac{1}{2}}{\left[{\mathrm{X}}_2\right]}^{\frac{1}{2}}---\left(1\right)$

Rate law (for slow step)

Rate = $\mathrm{K}\left[\mathrm{X}\right]\left[{\mathrm{Y}}_2\right]$

Substituting the value of  $\left[\mathrm{X}\right]$ from (1)

$\mathrm{rate}={\mathrm{KK}}_{\mathrm{eq}}^{\frac{1}{2}}{\left[{\mathrm{X}}_2\right]}^{\frac{1}{2}}\left[{\mathrm{Y}}_2\right]$

$\therefore \mathrm{order}\mathrm{w}.\mathrm{r}.\mathrm{t}{\mathrm{X}}_2=\frac{1}{2}$

$\mathrm{order}\mathrm{w}.\mathrm{r}.\mathrm{t}{\mathrm{Y}}_2=1$

Overall order = 1.5