Which of the following is the correct formula for copper (i) sulfate trihydrate? cuso4 · 3h2o
cuso4(h2o)3
cu2so4(h2o)3
cu2so4 · 3h2o

                   Cu₂SO₄ · 3 H₂O

                         First of all we should be interested in the oxidation number carried out by Copper atom because it can exist both in +1 and +2 state. Hence, as shown in name i.e. (I), it shows that copper is having +1 oxidation state.

                          Secondly, we should be interested in the charge carried out by sulfate ion, as it is conjugate base of sulfuric acid so, it must contain a charge of -2.

                           Therefore, to neutralize -2 charge of SO₄²⁻ ion we have to add two Cu⁺¹ ions hence,

                                             Cu₂SO₄

Furthermore, the number of water molecules are three as the word tri- specifies three.

                                        Cu₂SO₄ . 3 H₂O

                    In naming ionic compounds the positive part is named first followed by negative ion.