Which one of the following compounds will give orange precipitate when treated with 2, 4-dinitrophenyl hydrazine?

The product obtained from the electrolytic oxidation of acidified sulphate solutions, is :

The parameters of the unit cell of a substance are a = 2.5, b = 3.0, c = 4.0, $$\alpha$$ = 90$$^\circ$$, $$\beta$$ = 120$$^\circ$$, $$\gamma$$ = 90$$^\circ$$. The crystal system of the substance is :

The oxidation states of 'P' in H₄P₂O₇, H₄P₂O₅ and H₄P₂O₆, respectively, are :