Answer
a. $ 2.7 \times 10^{24} \space Li \space atoms$
b. $ 1.39 \times 10^{23} \space CO_2 \space molecules$
c. $ 0.013 \space mole \space of \space Cu$
d. $0.623 \space moles \space of \space C_2H_6$
Work Step by Step
1. Conversion factors:
$$1 \space mole \space of \space X = 6.02 \times 10^{23} \space of \space X$$
a. $$4.5 \space mole\space of \space Li \times \frac{6.02 \times 10^{23} \space Li \space atoms}{1 \space mole \space of \space Li} = 2.7 \times 10^{24} \space Li \space atoms$$
b. $$0.0180 \space mole\space of \space CO_2 \times \frac{6.02 \times 10^{23} \space CO_2 \space molecules}{1 \space mole \space of \space CO_2} = 1.39 \times 10^{23} \space CO_2 \space molecules$$
c. $$7.8 \times 10^{21} \space atoms \space of \space Cu \times \frac{1 \space mole \space of \space Cu}{6.02 \times 10^{23} \space Cu \space atoms} = 0.013 \space mole \space of \space Cu$$
d. $$3.75 \times 10^{23} \space molecules \space of \space C_2H_6 \times \frac{1 \space mole \space of \space C_2H_6}{6.02 \times 10^{23} \space C_2H_6 \space molecules} = 0.623 \space moles \space of \space C_2H_6$$
