Element of the third period that is expected to exhibit positive electron gain enthalpy is: 

The correct order of ionic radii is:

1. $H^{-}>H^{+}>H$ $$
2. $N{a}^{+}>F^{-}>O^{2-}$
3. $F^{-}>O^{2-}>N{a}^{+}$
4. $N^{3-}>M{g}^{2+}>A{l}^{3+}$

The formula for the oxide formed by Eka-aluminum is:

1. ${\mathrm{EO}}_4$

2. ${\mathrm{E}}_2{\mathrm{O}}_3$

3. ${\mathrm{E}}_3{\mathrm{O}}_2$

4. EO

The species Ar, K⁺ and Ca²⁺ contain the same number of electrons. In which order do their radii increase?
1.  Ar < K⁺ < Ca²⁺
2. Ca²⁺ < Ar < K⁺
3. Ca²⁺ < K⁺ < Ar
4. K⁺ < Ar < Ca²⁺

 The trend of atomic radius in a period and a group is :

The basic difference between the  electron gain enthalpy (E_a) and electronegativity (E_N) is: