Final answer:
The percent by mass of hydrogen in the compound is (12.9 g / 73.0 g) × 100%, which equals 17.7%. The correct answer is (a) 17.7%.
Step-by-step explanation:
To determine the percent by mass of hydrogen in the compound, we use the formula:
(mass of hydrogen / total mass of the compound) × 100%
In this case, we have 12.9 grams of hydrogen in a 73.0 gram sample of the compound. Therefore, the percent by mass of hydrogen is calculated as follows:
(12.9 g H / 73.0 g compound) × 100% = 17.7%
The correct answer is (a) 17.7%