Which of the following formulas must represent a molecular formula?

• A. H2O2
• B. CH2
• C. C2H6
• D. NaCl

Answer: (C)

Verified step by step guidance

1. Understand the difference between empirical and molecular formulas: An empirical formula shows the simplest whole-number ratio of atoms in a compound, while a molecular formula shows the actual number of atoms of each element in a molecule.
2. Analyze each given formula to determine if it can be simplified further: For example, CH2 can be simplified to CH2 (already simplest), but check if it represents the actual molecule or just the ratio.
3. Check if the formula represents a known molecule with whole numbers that cannot be reduced: H2O2 (hydrogen peroxide) has a molecular formula that cannot be simplified further, so it must be a molecular formula.
4. For C2H6, verify if it can be simplified: The ratio of carbon to hydrogen is 2:6, which simplifies to 1:3, so the empirical formula is CH3, meaning C2H6 is a molecular formula representing the actual molecule.
5. For NaCl, since it is an ionic compound, the formula represents the simplest ratio of ions and is considered an empirical formula, not a molecular formula.