Match List-I with List-II

	List-I (Ion)	List-II (Group Number in Cation Analysis)
A.	Co2+	I. Group-I
B.	Mg2+	II. Group-III
C.	Pb2+	III. Group-IV
D.	Al3+	IV. Group-VI

Choose the correct answer from the options given below:

The correct answer is A-III, B-IV, C-I, D-II.

In qualitative inorganic analysis, cations are classified into different groups based on their ability to form precipitates with specific group reagents under defined conditions. Let's analyze each of the given ions step-by-step:

1. Pb²⁺ (Lead ion):
Lead belongs to Group-I of the cation analysis scheme. The group reagent for Group-I is dilute hydrochloric acid (HCl). When dilute HCl is added to a solution containing Pb²⁺, it precipitates as white lead chloride (PbCl₂). Therefore, C matches with I.

2. Al³⁺ (Aluminium ion):
Aluminium belongs to Group-III of the cation analysis scheme. The group reagent is ammonium hydroxide (NH₄OH) in the presence of ammonium chloride (NH₄Cl). Under these conditions, aluminium precipitates as gelatinous white aluminium hydroxide, Al(OH)₃. Therefore, D matches with II.

3. Co²⁺ (Cobalt ion):
Cobalt belongs to Group-IV of the cation analysis scheme. The group reagent is hydrogen sulfide (H₂S) gas in the presence of ammonium hydroxide (NH₄OH) and ammonium chloride (NH₄Cl). Under alkaline conditions, cobalt precipitates as black cobalt sulfide (CoS). Therefore, A matches with III.

4. Mg²⁺ (Magnesium ion):
Magnesium belongs to Group-VI of the cation analysis scheme. It is identified by the formation of a white precipitate of magnesium ammonium phosphate, Mg(NH₄)PO₄, when treated with disodium hydrogen phosphate in the presence of ammonium hydroxide. Therefore, B matches with IV.

Summary of the correct matches:
• A. Co²⁺ ⇒ III. Group-IV
• B. Mg²⁺ ⇒ IV. Group-VI
• C. Pb²⁺ ⇒ I. Group-I
• D. Al³⁺ ⇒ II. Group-III