The number of molecules of a chemical substance that is equal to its molecular weight in grams is called a(n):

• A. mole
• B. atom
• C. ion
• D. formula unit

Answer: (A)

Verified step by step guidance

1. Understand that the question is asking for the term that describes the quantity of molecules equal to the molecular weight expressed in grams.
2. Recall that the molecular weight (or molar mass) of a substance is the mass of one mole of that substance, measured in grams per mole (g/mol).
3. Recognize that the term 'mole' is defined as the amount of substance containing exactly \$6.022 \times 10^{23}$ entities (Avogadro's number), which can be atoms, molecules, ions, or formula units depending on the substance.
4. Note that when you have a mass of a substance equal to its molecular weight in grams, you have exactly one mole of that substance, which corresponds to \$6.022 \times 10^{23}$ molecules.
5. Therefore, the correct term for the number of molecules equal to the molecular weight in grams is a 'mole'.