(b)
$5CO + I_{2}O_{5} \rightarrow 5CO_{2} + I_{2}$
1 mole of $I_{2} \equiv$1 moles of $I_{2}O_{5} \equiv$5 moles of CO
Hence, mole of CO=$5 \times \frac{2.54}{254} = 0.05$
Mass of CO=0.05$\times 28 = 1.4$g
Mass of $CO_{2} = 2 - 1.4 = 0.6$ g
Mass % of $CO_{2} = \frac{0.6 \times 100}{2} = 30$