Lewis Structure Example on page 79 of Course Reader

[Abbey Kerscher 3O]

On page 79 of the course reader, at the very bottom of the page, there is a diagram of how (NH4)2 SO4 should be portrayed with Lewis Structure. All of it made sense to me except there is the number 4 placed in front of the diagram showing SO4. Was that a typo or is there an actual reason that's there that I''m just not getting?

[Christian Hardoy 3F]

That 4 that you see on page 79 isn't part of the Lewis structures that are depicted there. If you look at the same spot on each page in each section there is a number indicating what page number you are on in the section. The number at the bottom right is the page number in the course reader and the number in the middle of the bottom third of the page, like the 4 on page 79, is the section page number.