Question

Nitrates of all metals are:
(A) unstable
(B) coloured
(C) insoluble in water
(D) soluble in water

Answer 1

Hint: Metal nitrates are the chemical compounds that contain Metal ions and nitrate ions $(N{O_3}^ - )$. The metal ions may be of Sodium, Potassium, caesium, Copper, etc. For Example-Lithium Nitrate $(LiN{O_3})$, Sodium Nitrate $(NaN{O_3})$, etc. These nitrates have important applications in the making of Fertilizers and are strong oxidizers hence used in making explosives.

Complete answer: Now let us look at all the options-
Option (A) says that Nitrates are Unstable. However, this is not true because some Nitrates like Sodium Nitrate, Potassium Nitrate, etc. are highly stable and can be found as such in nature.
Option (B) says that Nitrates are coloured. Some Nitrates are coloured for example-Copper nitrate is blue in color however all of them are not coloured for example-Silver nitrate and Zinc nitrate are colorless crystalline solids.
Option (C) says that Nitrates are insoluble in water. This is incorrect since most of the nitrates are soluble in water.
Option (D) says that Nitrates are soluble in water which is correct. The reason for the solubility of the Nitrates is because their Lattice energy is less than their solvation Energy. For Example- all Sodium and Potassium nitrates are soluble in water.
(Lattice Energy is the energy required to separate positive and negative ions in a lattice and solvation energy is the amount of energy associated with the dissolving of a solute in a solvent. The relation between lattice energy and solvation energy is very important to determine the solubility of Ionic compounds in water.)
Hence Option (D) is correct.

Note:
It is interesting to note that the Alkali Metal nitrates except that of Lithium Nitrate produce Nitrites and Oxygen gas. Alkaline Earth Metal nitrates on thermal decomposition produce Metal oxides, Brown Nitrogen dioxide, and Oxygen gas. The thermal stability of Metal nitrates increases from top to bottom in a group.