Question

Which of these have no unit
A.Electronegativity
B.Electron affinity
C.Ionisation energy
D.Excitation potential

Answer 1

Electronegativity is a relative term. It is the property of a bonded atom. The relative tendency of an atom to attract the shared pair of electrons toward itself is called electronegativity.

Complete answer:
Electronegativity is the tendency of the atom to attract the electrons towards itself when combined in a compound as defined by Pauling. Electronegativity is a relative term so it does not have any unit.
Electron affinity is the energy released when an electron is added to a gaseous atom which is in its ground state to form a gaseous negative ion is defined as the first electron affinity. The symbol is EA, and the unit of electron affinity is kJ/mol.
The ionization energy, EI, of an atom or an ion is the minimum energy that is required to remove an electron of an atom. The unit of ionization energy is kJ/mol.
Excitation Potential is the amount of energy that is required to raise the energy level of an atom; a necessity if the atom is to radiate energy. The amount of energy in the upper state of the transition involved in the production of a given spectral line is high excitation potential. The amount of energy, expressed in electron volts, needed to stimulate an atom to the state in which it can absorb the light of a given wavelength is low excitation potential.
Hence, electronegativity has no unit.

Therefore, the correct answer is option (A).

Note: The electronegativity of a non‐metal is larger than that of the metal. For the elements of one period, the electronegativity increases from left to right across the periodic table. For the elements of one main group, the electronegativity decreases from top to bottom across the periodic table. There is no regular rule to the subgroup elements.