Which of the following arrangements is correct for increasing order of electronegativity?

The correct sequence of increasing radii is:

Which one of the following represents all isoelectronic species?

The value of electron gain enthalpy of $Na^+$, if $IE_1$ of Na = 5.1 eV, is:

Be²⁺ is isoelectronic with which of the following ions?

Identify the correct order of the size of the following species: $Ca^{2+}, K^+, Ar, S^{2-}, Cl^-$

The formation of the oxide ion O²⁻(g) from oxygen atom requires first an exothermic and then an endothermic step as shown below: O(g) + e⁻ → O⁻(g); ΔH° = -141 kJ mol⁻¹ O⁻(g) + e⁻ → O²⁻(g); ΔH° = +780 kJ mol⁻¹ Thus, the process of formation of O²⁻ in gas phase is unfavourable even though O²⁻ is isoelectronic with neon. It is due to the fact that:

The correct order of decreasing second ionization enthalpy of Ti(22), V(23), Cr(24) and Mn(25) is:

Which of the following pair is correctly matched?