Twenty molecules of tetrasulfur tetranitrogen contain how many atoms of sulfur?

The correct answer is 80 atoms of sulfur.

In order to answer this question we must firstly find the molecular formula of tetrasulfur tetranitrogen. The said molecule has the molecular formula of S4N4.
Therefore, each molecule of S4N4 contains four atoms of sulfur (S).
If one molecule of S4N4 contains 4 sulfur atoms, then twenty molecules contain 
20 x 4= 80 atoms of sulfur.