Which reaction below represents the first electron affinity of rubidium?
(a) Rb(g) + e⁻ → Rb⁻(g)
(b) Rb(g) + e⁻ → Rb⁺(g)
(c) Rb(g) → Rb⁻(g) + e⁻
(d) Rb(g) → Rb⁺(g) + e⁻
(e) Rb(s) + e⁻ → Rb⁻(aq)