When iron is exposed to moisture and it rusts, the value of ΔG for the reaction is

The value of ΔG (change in Gibbs free energy) for a chemical reaction indicates whether the reaction is spontaneous or non-spontaneous. If ΔG is negative, the reaction is spontaneous, meaning it can occur without an external energy source. If ΔG is positive, the reaction is non-spontaneous, meaning it requires an external energy source to occur. If ΔG is zero, the reaction is at equilibrium. When iron rusts, it undergoes a chemical reaction with oxygen and water to form iron oxide (rust). This reaction is spontaneous, and as a result, the value of ΔG for the reaction is negative. Therefore, the correct answer to the question is "negative."