A mole of any substance always contains the same count of molecules

Evidence

The molecular mass of a gas is approximately equal to the total number of protons and neutrons in the molecule expressed in grams (g). Molecular mass expressed in this way always contains the same number of molecules (6.022 × 1023). This number of molecules is known as a “mole” (mol). — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 80

Categorization

• DEFINE: Standard chemistry definition; useful glossary-level clarification but very basic.
• corroborated: 2 independent passages support this claim — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 80