Which one among the following pairs is more electronegative and why?
(i) `C_(sp)` or `C_(sp^(3)),` (ii) carbon in `CHI_(3)` or carbon in `CHCl_(3)`,
(iii) Na or Cl (iv) carbon in `C_(2)H_(4) ` or `C_(2)H_(2)`.

Explanation

(i) `C_(sp)` is more electronegative than `C_(sp^(3))` because, for hybrid orbitals, electronegativity increases with incrase ini s-character of the hybrid orbital.
(ii) C in `CHCl_(3)` is more electronegative than C in `CHI_(3)` because, electronegativity of an atom increases with increase in s-character of the hybrid orbitals.
(ii) C in `CHCl_(3)` is more electronegative than C in `CHI_(3)` because, electronegativity of an atom increases with increase in electronegativity of the atom bonded to it.
(iii) Chlorine (Cl) is more electronegative than sodium (Na) because, as we move from left to right in a given period, atomic size decreases, and effective nuclear charge increases. hence electronegativity increases.
(iv) In `C_(2)H_(4),C` is `sp^(2)` hybridised while in `C_(2)H_(2),C` is sp hybridised. since electronegativity increases with increase in s-character of the hybrid orbitals, C in `C_(2)H_(2)` is more electronegative than `C` in `C_(2)H_(4)`.