Figure $1.$ A catalytic flow reactor having dimensions $WHL$ in the $x-,y-$ and z$-$directions such that $L>W$ and $W>H.$ Gaseous mixture of $CO$ and $H_{2}O$

enters the reactor through plane A and leaves through plane D$.$ Catalyst is coated on the bottom wall between planes B and $C$ which are at distances of $0\mathrm{.}5L$

and $0\mathrm{.}75L$ from the inlet. The reactor is pre$-$heated through the top and the bottom walls over the distance between planes A and $B.$

In Figure $1,$ which of the following statements is true in the Section AB assuming that a constant wall heat flux is imposed:

$($i$)$ cross$-$section averaged gas velocity remains constant

$($ii$)$ gas temperature will increase linearly

$($iii$)$ concentration of CH$4$ will decrease monotonically

$($i$)$ only

$($ii$)$ only

$($i$)$ & $($ii$)$

$($i$)$ & $($iii$)$