Final answer:
The correct statement among the options is a. 2nd electron gain enthalpy is always endothermic.
Step-by-step explanation:
The correct statement among the options is a. 2nd electron gain enthalpy is always endothermic.
The second electron gain enthalpy refers to the energy change that occurs when an atom gains its second electron to form a negative ion. Since adding an electron to an atom requires overcoming the repulsion between the incoming electron and the existing electrons, it is always an endothermic process. Therefore, option a is correct.
Options b, c, and d are incorrect. Electronegativity is the property of both covalently bonded and ionically bonded atoms. Amphoteric oxides are substances that can act as both acids and bases, whereas Al2O3 and BeO are only amphoteric. Therefore, option b and c are incorrect. Option d states that none of these statements are incorrect, which is incorrect because option a is correct.