Please help, I am struggling to understand the counting of atoms

Check Box 1 and Box 3

Explanation: Formula 1 has (NO3)2 meaning it has 6 oxygen atoms (2x6) while formula 2 has CO3 with only 3 oxygen atoms.

Its essentially the same thing with box 3 with there being 8 hydrogen in formula 2 (NH4)2 and only 4 in formula 5 NH4 by itself

organisms are more likely to be more preserved in mud than sand because mud is moist and wet, while sand is very dry.