NaCl H2SO4 KNO3 CaCl3
They are molecules.
Calcium chloride is better (the solubility heat is greater) but is more expensive.
CaCl3 does not exist, it is an impossible molecular formula.But if it were possible, then it would have been a salt, definitely soluble in water and it might possibly be hydrated in crystallised solid form with 2 molecules of H2O, if that is what you've meant by 'aqueous.However if you meant CaCl2: this is soluble salt (Calcium chloride) of which also mono-, di-, tetra-, and hexa-hydrates exist.
There are three atoms in CaCl2 (calcium chloride) - one calcium atom and two chlorine atoms. It might be argued that there are ions inside the molecule instead of atoms. In that case there is one calcium ion and two chlorine ions.