Which substance has Hf defined as 0 kJ/mol? H2O s Ne l O2 g CO2 g

Answer:O₂ (g).Explanation:All elements that found in nature has heat of formation (Hf) equal 0 J/mol.So, the substance that  has heat of formation (Hf) equal 0 J/mol is O₂ (g).H₂O is formed from the reaction of hydrogen and oxygen and has Hf, Also, the solidification of H₂O (s) from H₂O (l) has (Hf).Although, Ne (g) is found in nature and has no Hf, the liquification to form Ne (l) has heat of formation (Hf).CO₂ (g) is formed from the reaction between carbon and oxygen and so has heat of formation (Hf).