Consider the substances below.• 1 mol of beryllium• 1 mol of salt• 1 mol of water• 1 mol of hydrogenWhich statement is true about these substances?1) They have exactly the same mass. 2) They have different numbers of particles. 3) They have the same number of atoms. 4) They have different masses.

Your teacher probably expects you to say (correctly!) that 4) is true - They have different masses; But 2) is also true. One mole of beryllium, water, and hydrogen each contain Avogadro's number of particles. Salt, however, is an ionic compound. It contains Avogadro's number of sodium ions plus Avogadro's number of chloride ions (twice Avogadro's number of particles).