20. Electrochemistry

What is the oxidation number of each underlined element?

a) P₄                                  b) BO₃^3–                                c) AsO₄^2–                           d) HSO₄^–

In the following reaction identify the oxidizing agent and the reducing agent:

Cr₂O₇^2- + 6 Fe²⁺ + 14 H⁺ → 2 Cr³⁺ + 6 Fe³⁺ + 7 H₂O

3 Pb²+ (aq) + 2 Cr (s) → 3 Pb (s) + 2 Cr³⁺ (aq)

NO₃‾ (aq) + Cu (s) → NO (s) + Cu²⁺ (aq)