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) 

• A. I, II, III, IV
• B. I, II and III
• C. III
• D. I and II
• E. IV

Answer: (D)

Verified step by step guidance

1. Identify the key characteristic of an oxidation-reduction (redox) reaction: it involves the transfer of electrons between species, resulting in a change in oxidation states.
2. Examine reaction I: PCl3 (aq) + Cl2 (g) → PCl5 (aq). Determine the oxidation states of phosphorus and chlorine before and after the reaction. If there is a change in oxidation states, it is a redox reaction.
3. Examine reaction II: 2 AgNO3 (aq) + Cu (s) → Cu(NO3)2 (aq) + 2 Ag (s). Determine the oxidation states of silver and copper before and after the reaction. Look for changes in oxidation states to identify it as a redox reaction.
4. Examine reaction III: CO2 (g) + 2 LiOH (aq) → Li2CO3 (aq) + H2O (l). Check the oxidation states of carbon, lithium, and oxygen before and after the reaction. If there are no changes in oxidation states, it is not a redox reaction.
5. Examine reaction IV: FeCl2 (aq) + 2 NaOH (aq) → Fe(OH)2 (aq) + 2 NaCl (aq). Determine the oxidation states of iron, sodium, and chlorine before and after the reaction. If there are no changes in oxidation states, it is not a redox reaction.