How many atoms of oxygen in 4 molecules of \( \mathrm{HNO}_{3} \) ? \( \begin{array}{l}\text { a } 7.2 \times 10^{24} \\ \text { b } 12 \\ \text { c } 2.4 \times 10^{24} \\ \text { d } 7\end{array} \)

Each molecule of \( \mathrm{HNO}_{3} \) contains 3 oxygen atoms. Therefore, in 4 molecules, the total number of oxygen atoms can be calculated as follows: \( 4 \times 3 = 12 \). So the correct answer is \( \text{b } 12 \). Understanding how to determine the number of atoms in a compound can help in various fields including chemistry, biology, and environmental science. This foundational knowledge is crucial when tackling complex topics like stoichiometry, chemical reactions, and understanding molecular structures. As a problem-solving tip, always remember to break down the question into manageable parts. First, identify the number of atoms in one molecule, then multiply by the number of molecules, like we did here. A common mistake is to forget this step and try to guess or skip to the final answer!