Question

How many sodium atoms are represented in the formula `7Na_3PO_4`?

Answer 1

What is `7xx3?`

Explanation:

In one formula unit of `Na_3PO_4`, clearly there are 3 sodium atoms, 1 phosphorus atom, and 4 oxygen atoms. Do you agree?

So if we have seven formula units of `Na_3PO_4`, there are `7xx3` sodium atoms, `7xx1` phosphorus atoms, and `7xx4` oxygen atoms.