Question

The alkaline earth metal nitrate that does not crystallize with water molecules
A.$Sr{(N{O_3})_2}$
B.$Mg{(N{O_3})_2}$
C.$Ca{(N{O_3})_2}$
D.$Ba{(N{O_3})_2}$

Answer 1

To answer this question, you should recall the concept of properties of alkaline earth metal nitrates. You should know about the effect of cation on the tendency of its salt to crystallize with water.

Complete step by step answer:
Alkaline Earth metals are $Be,Mg,Ca,Sr,Ba,Ra$. These elements are electro-positive and possess two electrons in their outermost shell making them highly reactive. From the nitrates of alkaline earth metals, Barium Nitrate does not crystalline with molecules of water.
The reason for this effect is due to size disparity as size increases as we move down the group. This salt is highly soluble in water due to less lattice enthalpy. Polar ions of nitrate anion attract the polar molecules of water and as the size of the cation is very large very fewer molecules will crystallize.

Hence, the correct answer is option D barium nitrate $Ba{\left( {NO3} \right)_2}$.

Note:
You should know about how water molecules are held in the water of crystallization. The water of crystallisation is referred to as the number of water molecules present in one formula unit of salt.
For example: $CaS{O_4}.2{H_2}O$ is called calcium sulphate dihydrate and it has 2 molecules of water of crystallization. These water molecules are held together with the compound by the special bonding called hydrogen bonding. The hydrogen bonding is a type of weak force that results in the formation of dipole-dipole interaction between a hydrogen atom and an electronegative atom that is strongly bonded to another electronegative atom. The bond or bonds are mostly strong in comparison to normal dipole-dipole and dispersion forces. Crystalline salts frequently contain water in two different states of combination, which are distinguished by the terms water of constitution and water of crystallization.