Which reaction below represents the electron affinity of potassium (K)?

• A. K(g) → K^+(g) + e^-
• B. K^+(g) + e^- → K(g)
• C. K(g) + e^- → K^-(g)
• D. K(s) + e^- → K^-(g)

Answer: (C)

Verified step by step guidance

1. Understand that electron affinity refers to the energy change when a neutral atom in the gas phase gains an electron to form an anion.
2. Identify that the species must be in the gaseous state because electron affinity is defined for isolated atoms or ions in the gas phase.
3. Recognize that the reaction should show a neutral atom gaining an electron, which can be written as \(K(g) + e^- \rightarrow K^-(g)\).
4. Compare the given reactions: the first shows potassium losing an electron (ionization), the second shows a cation gaining an electron (recombination), and the last involves potassium in solid state, which is not relevant for electron affinity.
5. Conclude that the correct representation of electron affinity is the reaction where gaseous potassium atom gains an electron to form the potassium anion in the gas phase.