One litre of a mixture of $CO$ and $C{O}_2$ is passed over red hot coke when the volume increased to $1.6$ L under the same conditions of temperature and pressure. The volume of $CO$ in the original mixture is

$C{O}_2$ (g) + $C$(s) --------> $2CO$ (g)

V = initial volume of $C{O}_2$ – reacted volume of $C{O}_2$ = $(1 -x) L$

$(1-x)+2x=1.6$

$1+x=1.6$

$x=1.6-1/2$

$x=0.3$

Volume of carbon dioxide is $0.3L$

Volume of $CO$ = $2x = 2x 0.3 = 0.6L$

$0.6L = 600ml$

Hence, the correct option is B.