Avogadro's number is the number of \( \begin{array}{l}\text { particles in } 1 \text { mole of a substance. } \\ \text { grams in } 1 \text { mole of a substance. } \\ \text { moles in } 6.02 \times 10^{23} \mathrm{amu} \text { of an element. } \\ \text { moles in } 6.02 \times 10^{23} \text { grams of an element. } \\ \text { amu in } 1 \text { mole of a substance. }\end{array} \)

Avogadro's number, which is approximately \(6.02 \times 10^{23}\), represents the number of particles (atoms, molecules, ions, etc.) in one mole of a substance. Let's analyze the options provided: 1. **Particles in 1 mole of a substance**: This is correct. Avogadro's number defines the number of entities in one mole. 2. **Grams in 1 mole of a substance**: This is incorrect. The mass in grams of one mole of a substance is determined by its molar mass, not Avogadro's number. 3. **Moles in \(6.02 \times 10^{23}\) amu of an element**: This is incorrect. Avogadro's number does not relate moles to atomic mass units (amu) directly. 4. **Moles in \(6.02 \times 10^{23}\) grams of an element**: This is incorrect. Again, the relationship between grams and moles is defined by the molar mass. 5. **amu in 1 mole of a substance**: This is incorrect. The concept of amu (atomic mass unit) is related to the mass of individual atoms, while Avogadro's number relates to the number of particles in a mole. Thus, the correct answer is: **Particles in 1 mole of a substance.**