The compound YBa₂Cu₃O₇, which shows superconductivity, has copper in oxidation state ______ assume that the rare earth element yttrium is in its usual +3 oxidation state.

8.0575 $$\times$$ 10^-2 kg of Glauber's salt is dissolved in water to obtain 1 dm³ of a solution of density 1077.2 kg.m^-3. Calculate the molarity, molality and mole fraction Na₂SO₄ in the solution.

The outermost electronic configuration of Cr is _______.

Find out the number of waves made by a Bohr electron in once complete revolution in its 3rd orbit?