Answer
a.$$ 2.74 \times 10^{21} \space molecules $$
b.$$ 1.94 \times 10^{21} \space molecules $$
c.$$ 4.24 \times 10^{21} \space molecules $$
Work Step by Step
a. - Using the molar mass as a conversion factor, find the amount in moles:
$$ 1.00 \space g \times \frac{1 \space mole}{ 219.88 \space g} = 0.00455 \space mole$$
$$ 0.00455 \space mole \space \times \frac{6.02 \times 10^{23} \space molecules }{1 \space mole} = 2.74 \times 10^{21} \space molecules $$
b.$$ 1.00 \space g \times \frac{1 \space mole}{ 310.18 \space g} = 0.00322 \space mole$$
$$ 0.00322 \space mole \space \times \frac{6.02 \times 10^{23} \space molecules }{1 \space mole} = 1.94 \times 10^{21} \space molecules $$
c.$$ 1.00 \space g \times \frac{1 \space mole}{ 141.96 \space g} = 0.00704 \space mole$$
$$ 0.00704 \space mole \space \times \frac{6.02 \times 10^{23} \space molecules }{1 \space mole} = 4.24 \times 10^{21} \space molecules $$
