Which of the following statements about naming molecular compounds is correct?

• A. Ionic charges are indicated using Roman numerals in the names of molecular compounds.
• B. The metal is always named first in molecular compounds.
• C. Molecular compounds never use the prefix 'mono-' for the first element.
• D. Prefixes are used to indicate the number of atoms of each element in the compound.

Answer: (D)

Verified step by step guidance

1. Step 1: Understand that molecular compounds are typically formed between nonmetal elements, and their naming follows specific rules different from ionic compounds.
2. Step 2: Recall that ionic charges indicated by Roman numerals are used in naming ionic compounds, especially transition metals, not molecular compounds.
3. Step 3: Recognize that in molecular compounds, the more electropositive element (usually the one farther left or lower on the periodic table) is named first, but this does not necessarily mean a metal is involved, as molecular compounds are usually nonmetals.
4. Step 4: Know that the prefix 'mono-' is generally omitted for the first element if there is only one atom, but it is used for the second element to indicate the number of atoms.
5. Step 5: Conclude that the correct naming rule for molecular compounds is that prefixes (mono-, di-, tri-, etc.) are used to indicate the number of atoms of each element in the compound.