The surface of copper gets tarnished by the formation of copper oxide. N2 gas was passed to prevent the oxide formation during heating of copper at 1250 K. However, the N2 gas contains 1 mole % of water vapour as impurity. The water vapour oxidises copper as per 2Cu(s) + H2O(g) → Cu2O(s) + H2(g). pH2 is the minimum partial pressure of H2 (in bar) needed to prevent the oxidation at 1250 K. The value of ln(pH2) is ____. (Given: total pressure = 1 bar, R = 8 J K−1 mol−1, ln(10) = 2.3, Cu(s) and Cu2O(s) are mutually immiscible. At 1250 K: 2Cu(s) + 1/2 O2(g) → Cu2O(s), ΔG° = −78,000 J mol−1; H2(g) + 1/2 O2(g) → H2O(g), ΔG° = −1,78,000 J mol−1.)