Answer:
d.57.2%
Explanation:
Given,
Moles of
= 6.85 moles
Moles of
= 24.9 moles
According to the given reaction:

1 mole of
reacts with 5 moles of 
6.85 moles of
reacts with 5*6.85 moles of 
Moles of
= 34.25 moles
Available moles of
= 24.9 moles
Limiting reagent is the one which is present in small amount. Thus,
is limiting reagent.
The formation of the product is governed by the limiting reagent. So,
5 moles of
produces 3 moles of 
1 mole of
produces 3/5 moles of 
24.9 moles of
produces (3/5)*24.9 moles of 
Moles of
produced = 14.94 moles
The expression for the calculation of the percentage yield for a chemical reaction is shown below as:-

Theoretical yield = 14.94 moles
Given, Experimental yield = 8.55 moles
Applying the values in the above expression as:-

