Answer
a.
$$1.10 \times 10^{22} \space atoms \space P$$
b.
$$3.88 \times 10^{21} \space atoms \space P$$
c.
$$4.24 \times 10^{21} \space atoms \space P$$
Work Step by Step
1. Using the answers from exercise 60:
a. Each $P_4O_6$ has 4 $P$:
$$2.74 \times 10^{21} \space molecules \space P_4O_6 \times \frac{4 \space atoms \space P}{1 \space molecule \space P_4O_6} = 1.10 \times 10^{22} \space atoms \space P$$
b. Each $Ca_3(PO_4)_2$ has 2 $P$:
$$1.94 \times 10^{21} \space molecules \space Ca_3(PO_4)_2 \times \frac{2 \space atoms \space P}{1 \space molecule \space Ca_3(PO_4)_2} = 3.88 \times 10^{21} \space atoms \space P$$
c. Each $Na_2HPO_4$ has 1 $P$:
$$4.24 \times 10^{21} \space molecules \space Na_2HPO_4 \times \frac{1 \space atom \space P}{1 \space molecule \space Na_2HPO_4} = 4.24 \times 10^{21} \space atoms \space P$$
