Final answer:
Electronegativity is the tendency of an atom in a compound to attract bonding electrons and is calculated on a relative scale, while electron gain enthalpy is the energy change when an electron is added to a gaseous atom and is measured in kJ/mol. The correct options distinguishing these concepts are A and B.
Step-by-step explanation:
Electronegativity and electron gain enthalpy are two different concepts in chemistry that are often confused. Electronegativity is a measure of an atom's tendency to attract a bonding pair of electrons when it is part of a compound. This is a dimensionless quantity and is determined using a relative scale devised by Linus Pauling, the most common being the Pauling scale, which compares all elements to fluorine, the element with the highest assigned value of 3.98.
Electron gain enthalpy, also known as electron affinity, is the energy change that occurs when an electron is added to a neutral atom in the gaseous state to form a negative ion. It is a measurable physical property, often released and sometimes absorbed, expressed in units of kilojoules per mole (kJ/mol).
Considering your choices, the correct options identifying the differences between electron gain enthalpy and electronegativity are:
A. Electron gain enthalpy is an energy change during the addition of an electron, while electronegativity is a measure of an atom's tendency to attract shared electrons in a chemical bond.
B. Electron gain enthalpy is an absolute quantity, while electronegativity is a relative measure that compares the electron-attracting ability of different elements.
Therefore, the mention of the correct option in the final answer, reflecting the difference between these two properties, includes both option A and option B.