Concept:A reaction is spontaneous when it can proceed without external energy input.
Explanation:Gibbs free energy is written as
ΔG.
It measures the useful energy available during a reaction at constant temperature and pressure.
If
ΔG is negative, the reaction releases free energy and moves to a more stable state.
This makes the reaction naturally favourable, so it is spontaneous.
If
ΔG is positive, the reaction needs external energy and is non-spontaneous.
If
ΔG is zero, the system is at equilibrium, not a spontaneous change.
Therefore, for spontaneity,
ΔG must be less than zero.
Answer:ΔG must be negative.
Correct option: B.