$4.$For the elementary reaction A$+2$ B$<>$C$+$ D

$4\mathrm{.}1.$Write an expression for the rate of reaction of A$.($Use $+1$ or $-1$ to indicate a $+$ve or $-$ve sign.$)$rA $=$ kf CA CB$+$ kr CC CD

$4\mathrm{.}2.$What are the units of the rate constants in your rate equation? $($Use mol, L and s$)$

$4\mathrm{.}3.$Express rB in terms of rA$.($Use $+1$ or $-1$ to indicate a $+$ve or $-$ve sign.$)$

$4\mathrm{.}4.$Express rC in terms of rA$.($Use $+1$ or $-1$ to indicate a $+$ve or $-$ve sign.$)$

$4\mathrm{.}5.$Express rC in terms of rD$.($Use $+1$ or $-1$ to indicate a $+$ve or $-$ve sign.$)$