Treatment of a gas 'X' with a freshly prepared ferrous sulphate solution gives a compound 'Y' as a brown ring. The compounds X and Y are.

The brown ring test is a qualitative test used for the detection of nitrate ((NO_3^-)) or nitrite ((NO_2^-)) ions.

In the first step, nitrate ions are reduced by ferrous ions in the presence of dilute sulphuric acid to produce nitric oxide:

$$NO_3^-+3Fe^{2+}+4H^+\rightarrow NO+3Fe^{3+}+2H_2O.$$

Thus, gas (X) is nitric oxide ((NO)).

The nitric oxide formed then reacts with excess hydrated ferrous ions to produce the characteristic brown nitrosyl complex:

$$[Fe(H_2O)_6]^{2+}+NO\rightarrow[Fe(H_2O)_5(NO)]^{2+}+H_2O.$$

This complex is commonly represented as

$$[Fe(H_2O)_5(NO)]SO_4,$$

or simply

$$[Fe(NO)]SO_4.$$

Hence,

• (X = NO)
• (Y = [Fe(H_2O)_5(NO)]SO_4) (or ([Fe(NO)]SO_4))

Therefore, the correct answer is Option A.