What is the basic difference between the terms electron gain enthalpy and electronegativity?

Which one of the following sets of ions represents the collection of isoelectronic species?

The electronic configurations of $4$ atoms are given below:
$P = [Ne] \, 3s^2 3p^3$
$Q = [Ar] \, 3d^{10} 4s^2 4p^3$
$R = [He] \, 2s^2 2p^5$
$S = [Ne] \, 3s^1$
Which of the following statements is incorrect?

An element of atomic weight $40$ has $2, 8, 8, 2$ as the electronic configuration. Which one of the following statements regarding this element is not correct?

Which of the following orders is correct according to the given property?

Which of the following statements are correct?
$A.$ The process of the addition of an electron to a neutral gaseous atom is always exothermic.
$B.$ The process of removing an electron from an isolated gaseous atom is always endothermic.
$C.$ The $1^{st}$ ionization energy of boron is less than that of beryllium.
$D.$ The electronegativity of $C$ is $2.5$ in $CH_4$ and $CCl_4$.
$E.$ $Li$ is the most electropositive among elements of group $I$.
Choose the correct answer from the options given below: