In each of the following, tell whether the substance gains electrons or loses electrons in a redox reaction:

a. An oxidizing agent

b. A reducing agent

c. A substance undergoing oxidation

d. A substance undergoing reduction

Which element is being reduced in the following reaction? 

Cr₂O₇^2- + 3 HNO₂ + 5 H⁺ → 2 Cr³⁺ + 3 NO₃^- + 4 H₂O

Identify the oxidizing agent and reducing agent from the following redox reaction. 

Ba (s) + Cl₂ (g) → BaCl₂ (aq)

Which of the following represents an oxidation-reduction reaction? 

I. PCl₃ (aq) + Cl₂ (g) → PCl₅ (aq) 

II. 2 AgNO₃ (aq) + Cu (s) → Cu(NO₃)₂ (aq) + 2 Ag (s) 

III. CO₂ (g) + 2 LiOH (aq) → Li₂CO₃ (aq) + H₂O (l)

IV. FeCl₂ (aq) + 2 NaOH (aq) → Fe(OH)₂ (aq) + 2 NaCl (aq) 

Identify the oxidized reactant, the reduced reactant, the oxidizing agent, and the reducing agent in the following reactions:

a. Fe(s) + Cu²⁺(aq) → Fe²⁺(aq) + Cu(s)

b. Mg(s) + Cl₂(g) → MgCl₂(s)

c. 2 Al(s) + Cr₂O₃(s) → 2 Cr(s) + Al₂O₃(s)

Potassium, a silvery metal, reacts with bromine, a corrosive, reddish liquid, to yield potassium bromide, a white solid. Write the balanced equation, and identify the oxidizing and reducing agents.

Identify each of the following as an oxidation or a reduction:

c. Cr³⁺(aq) + 3e^– → Cr(s)