Question

The minimum equivalent conductance in fused state is shown by:
A.$MgC{l_2}$
B.$BeC{l_2}$
C.$CaC{l_2}$
D.$SrC{l_2}$

Answer 1

Hint: To answer this question, you should recall the trends in the periodic table. The modern periodic law developed by Moseley states that the physical and chemical properties of elements are the periodic function of their atomic number. As we move down the group, ionic character increases and the molecule dissociates more easily.

Complete answer:
When a salt is dissolved in a solvent the strong forces of attraction of solute must be overcome by the interactions between ions and the solvent. The solvation enthalpy of ions is always negative which means that energy is released during this process. The nature of the solvent determines the amount of energy released during solvation that is solvation enthalpy. According to Fajan’s rule:
Smaller the size of cation, more large the size of the anion will result in a more covalent character of the ionic bond.
More the charge density of cation, greater is the covalent character of the ionic bond.
Electronic configuration: For cations with same charge and size, the one, with \[\left( {n - 1} \right){d^{n}}n{s^o}\]which is found in transition elements have greater covalent character than the cation with \[n{s^{2}}n{p^6}\]electronic configuration, generally present s- block elements.
These cations belong to the same group i.e. group 2. On moving downward in a group, atomic size increases hence the covalent character decreases. Thus, $SrC{l_2}$ is most ionic among the given compounds and will give ions readily when it is in a fused state.

Hence, the correct option is option B.

Note: Let us summarize the trends of fundamental properties of an element: Atomic Radii and Ionic radii: The atomic radii and ionic radii of elements decrease while moving from left to right in a period. Ionization Enthalpy: Across a period in the periodic table, ionization energy generally increases. For the trend in a group, ionization enthalpy decreases from top to bottom. Electron gain enthalpy: Electron gain enthalpy becomes more negative as we move from left to right in a period. Electron gain enthalpy is negative when energy is released while accepting an electron. While it is positive when energy is supplied to an atom while adding an electron.