How many molecules are in 2.50 moles of O2

There are 6.022×1023 O2 molecules in a mole of O2. Since you have 2 oxygen atoms in one O2 molecule, there are 2×6.022×1023 O atoms in a mole of O2.

water and alcohols have similar properties because water molecules contain hydroxyl groups that can form hydrogen bonds with other water molecules and with alcohol molecules, and likewise alcohol molecules can form hydrogen bonds with other alcohol molecules as well as with water.