Complex sentence: Ruthenium tetroxide is reduced by cold dilute potassium hydroxide to form black potassium perruthenate, KRuO 4, with ruthenium in the +7 oxidation state: this can also be formed by oxidising potassium ruthenate, K 2 RuO 4, using chlorine gas.
Split into simpler sentences: Ruthenium tetroxide is reduced by cold dilute potassium hydroxide to form black potassium perruthenate, KRuO 4, with ruthenium in the +7 oxidation state. Potassium perruthenate can also be produced by oxidising potassium ruthenate, K 2 RuO 4, with chlorine gas.