Correct Answer - B
`SO_(3)(g)hArrSO_(2)(g)+(1)/(2)O_(2)(g)`
`{:(t=0,a,,0,0),(t=t_(eq),a-aalpha,,aalpha,(aalpha)/a):}`
Using: `n_(0)/n_(mix)=((M_(0))_(mix, f))/((M_(0))_(mix, i)) …(i)`
and `PM_(0)=dRT`
`rArr 1.2xxM_(0)=0.9xx0.08xx1000`
`rArr M_(0)=60 g "mol"^(-1)`
Substituting in equilibrium (i), we get
`rArr 1/(1+alpha/2)=60/80rArr alpha=2(80/60-1)=2/3`