Answer:
4
Explanation:
There are 4 different elements in the compound (N, H, P, O) but if you want to count the number of each element then the answer is different.
In NH4, theres 1 N and 4 H, but since there are 3 NH4s then u have 3 N and 12 H. There's 1 P and 4 Os as well.
Added together u have 3 + 12 + 1 + 4 = 20 elements in total.
hope this helps!
