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 1st ionization energy of the boron is less than that of the 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

The periodic properties involved in the five statements are electron affinity, ionisation enthalpy, electronegativity and electropositivity. We examine each one separately.

Case A: “The process of the addition of an electron to a neutral gaseous atom is always exothermic.”
Adding an electron to some atoms (for example $$Be,\,Mg,\,N,\,P$$ and the noble gases) is endothermic because the incoming electron must be placed either in a higher-energy subshell or into a completely new shell that is already shielded. Hence electron-gain enthalpy is not always negative.
Statement A is false.

Case B: “The process of removing an electron from an isolated gaseous atom is always endothermic.”
Ionisation energy (first ionisation enthalpy) is the energy required to pull an electron out of the attraction of the nucleus in the gaseous state. Work must always be done on the system, so the process is always endothermic (positive enthalpy change).
Statement B is true.

Case C: “The 1st ionization energy of boron is less than that of beryllium.”
Electronic configurations:
$$Be: 1s^2\,2s^2$$  ($$2s$$ subshell is fully filled and comparatively stable)
$$B : 1s^2\,2s^2\,2p^1$$  (the outermost electron is in a higher-energy $$2p$$ subshell)
It is easier to remove the lone $$2p$$ electron of boron than a $$2s$$ electron of beryllium, so $$IE_1(B) \lt IE_1(Be)$$.
Statement C is true.

Case D: “The electronegativity of C is 2.5 in $$CH_4$$ and $$CCl_4$$.”
Pauling electronegativity of carbon is quoted as 2.5 (more precisely 2.55). However, electronegativity is an empirical property that can vary slightly with the molecular environment, oxidation state and hybridisation. In $$CCl_4$$, carbon is strongly electron-deficient due to four $$Cl$$ atoms pulling electron density away, so its effective electronegativity is not the same numerical value that is assigned to carbon in non-polar $$CH_4$$. Thus the given fixed value “2.5” for both molecules is not strictly correct.
Statement D is false.

Case E: “Li is the most electropositive among elements of group I.”
Electropositivity (tendency to lose an electron) increases down the group because atomic size grows and ionisation energy decreases. Therefore $$Cs$$ (and then $$Rb,\,K,\,Na$$) are more electropositive than $$Li$$.
Statement E is false.

Only statements B and C are correct. Hence the correct choice is:

Option A: B and C only