Question

In which of the following order of Hydration energy is correct?

• A. ${\mathrm{Li}}^{+}>{\mathrm{Na}}^{+}>{\mathrm{K}}^{+}>{\mathrm{Rb}}^{+}>{\mathrm{Cs}}^{+}$
• B. ${\mathrm{Li}}^{+}<{\mathrm{Na}}^{+}<{\mathrm{K}}^{+}<{\mathrm{Rb}}^{+}<{\mathrm{Cs}}^{+}$
• C. ${\mathrm{Li}}^{+}>{\mathrm{Na}}^{+}>{\mathrm{K}}^{+}>{\mathrm{Cs}}^{+}>{\mathrm{Rb}}^{+}$
• D. ${\mathrm{Li}}^{+}<{\mathrm{Na}}^{+}<{\mathrm{K}}^{+}<{\mathrm{Cs}}^{+}<{\mathrm{Rb}}^{+}$

Answer 1

The correct option is A

${\mathrm{Li}}^{+}>{\mathrm{Na}}^{+}>{\mathrm{K}}^{+}>{\mathrm{Rb}}^{+}>{\mathrm{Cs}}^{+}$

Explanation for the correct option:

The correct option is A.

1. The hydration energy is inversely proportional to the size of the atom of elements.
2. When we move down the group the size increase and hydration energy will decrease down the group.
3. They all belong to group 1 of the periodic table.
4. Because in option A the size increases from Lithium to Cesium.
5. Therefore, increase in size the hydration energy decreases.
6. Therefore, option A is correct $({\mathrm{Li}}^{+}>{\mathrm{Na}}^{+}>{\mathrm{K}}^{+}>{\mathrm{Rb}}^{+}>{\mathrm{Cs}}^{+})$.
7. All other options do not fully fill this requirement thus they are incorrect.