Q$.$ A reactor is used to remove SiO$2$ from a wafer in semiconductor manufacturing by

contacting the SiO$2$ surface with HF$.$ The reactions are:

$6$HF$($g$)+$ SiO$2($s$)->$ H$2$SiF$6($l$)+2$H$2$O$($l$)$

H$2$SiF$6($l$)->$ SiF$4($g$)+2$HF$($g$)$

Assume the reactor is loaded with wafers having a silicon oxide surface, a flow of $50\%$ HF and

$50\%$ nitrogen is started, and all the H$2$SiF$6$ reacts. In the reaction $10\%$ of the HF is consumed.

What is the composition of the exhaust stream?