1. Determine the oxidation states of the elements in the compounds and on their basis indicate which of these compounds can be only oxidants, which - only reducing agents, and which are capable of disproportionation. Chromium in compounds
K2Cr2O7, [Cr(H2O)6]Cl3, Cr(OH)2, Cr, BaCrO4;

2. Determine the oxidation states of atoms and indicate which process (oxidation or reduction) occurs as a result of the transition.
HAsO4^2– → AsH3;

3. Based on the method of electronic balance, arrange the coefficients in the equation of redox reaction; indicate which substance is an oxidant and which is a reducing agent, which compound is oxidized and which is reduced; indicate to which type of redox reactions the given reaction belongs.
HNO3 → NO2 + O2+ H2O