Final answer:
One mole contains 6.02 X 10²³ molecules, which is known as Avogadro's number, a foundational constant in chemistry that allows for the conversion between mass and number of molecules.
Step-by-step explanation:
The student's question is, "How many molecules are contained in one mole?" The answer is the first option: 1) 6.02 X 10²³. This number is known as Avogadro's number, and it is a fundamental constant in chemistry. One mole of any substance, be it atoms, molecules, or particles, contains exactly this many entities. To remember this, it's helpful to know that 6.022 x 10²³ molecules (or other particles) make up a mole, although the official value with more precision is 6.02214076 x 10²³.
Using the mole concept, chemists can easily convert between the mass of a substance and the number of molecules it contains. For instance, if you have a substance with a known molar mass, you can calculate how many molecules are in a given sample by multiplying the amount (in moles) by Avogadro's number.