1Initially ... put PV = nRT .... (1)
Finally .... put (P/2)V = (n1+n2)RT ... (2)
From (2) .... PV = 2(n1+n2)RT
Now solving (1) and (2) ... 2(n1+n2) = n ... (3)
U need to find ... (n - n1)/n
3C2H2 --> C6H6
Let x moles react ...
3 moles of C2H2 gives 1 mole of C6H6 ...
Therefore x moles give x/3 moles of C6H6 ....
n-n1 = x
n2 = x/3
from (3) ...
n1 = x/3 ...
n = 2(x/3 + x/3)
n = 4x/3 ....
Hence reqd. ans is ...
4x/3 - x/34x/3 = 3/4 = 75%