#### Answer

a) Ca - 1 atom ; N - 2 atoms ; O -4 atoms
b) Cu - 1 atom ; S - 1 atom ; O - 4 atoms
c) Al - 1 atom ; N - 3 atoms ; O - 9 atoms
d) Mg - 1 atom ; H - 2 atoms ; C -2 atoms ; O - 6 atoms

#### Work Step by Step

a) In the formula, we can see that there is 1 atom of Ca, 2 atoms of $N$ (1x2), and 4 atoms of $O$ (2x2).
b) In the formula, we can see that there is 1 atom of Cu, 1 atom of $S$ and 4 atoms of $O$
c) In the formula, we can see that there is 1 atom of Al, 3 atoms of $N$ (1x3), and 9 atoms of $O$ (3x3)
d) In the formula, we can see that there is 1 atom of Mg, 2 atoms of $C$ (1x2), 2 atoms of $H$ (1x2), and 6 atoms of $O$ (3x2)