This is an incomplete question, here is a complete question.
The balanced chemical reaction is:
In another experiment, if 80 
molecules react with 104 
molecules. How many 
molecules will be produced which reactant will be used up in the reaction.
Answer : The number of molecules of will be, 52 molecules and reactant will be used up in the reaction because it is a limiting reagent and it limits the formation of product.
Explanation :
The balanced chemical reaction is:
First we have to determine the limiting reagent.
From the balanced reaction we conclude that,
As, 8 molecules of react with 6 molecule of
So, 104 molecules of react with 
molecule of
From this we conclude that, is an excess reagent because the given moles are greater than the required moles and is a limiting reagent and it limits the formation of product.
Now we have to calculate the molecules of
From the reaction, we conclude that
As, 8 molecules of react to give 4 molecules of
So, 104 molecules of react to give 
molecules of
Hence, the number of molecules of will be, 52 molecules and reactant will be used up in the reaction because it is a limiting reagent and it limits the formation of product.
