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.