Ethylene oxide is a high volume chemical intermediate that is used to produce glycol and polyethylene glycol. Ethylene oxide is produced by the partial oxidation of ethylene using a solid catalyst in a fixed bed reactor:

C$2$H$4+(1)/(2)$O$2->$ C$2$H$40$

In addition, a portion of the ethylene is combusted:

C$2$H$4+302->2$ CO$2+2$ H$20$

The product gas leaving the reactor has the following water$-$free composition:

$17\mathrm{.}5\%$ C$2$H$40,72\mathrm{.}7\%$ N$2,2\mathrm{.}3\%$ Oz$,3\mathrm{.}0\%$ C$2$H$4,$ and $4\mathrm{.}5\%$ COz.

Determine the $\%$ excess O$2$ in the feed.