What has more particles a mole of Helium atoms or a mole of water (H2O)?

A mole of water.

Explanation:

Helium is composed of stable atoms. That means you just have 1 mole particles. But with water, you have the molecules - 1 mole, and the atoms. There are 3 atoms in a molecule of water, so there are 3 mol atoms in 1 mol of H2O.

Helium: 1 mol particles

Water: 1 mol molecules + 3 mol atoms = 4 mol of distinguishable particles