Chemistry - Thermochemistry Question with Solution | TestHub

(a) This reaction is the reverse of the ionization of potassium (K), which is an exothermic process.

(b) This reaction represents the electron gain of chlorine (Cl), which is also an exothermic process.

(c) The sublimation of sodium requires energy, meaning ΔH > 0. Therefore, this option is ruled out.

(d) This reaction describes the formation of the MgCl₂ lattice from gaseous ions, where ΔH = -U < 0.

The correct answers are (a), (b), and (d).