Given below are certain cations. Using inorganic qualitative analysis, arrange them in increasing group number from 0 to VI.

A.   Al³⁺               B.   Cu²⁺

C.   Ba²⁺              D.   Co²⁺

E.   Mg²⁺

Choose the correct answer from the options given below.

To arrange the given cations in increasing order of their group numbers in inorganic qualitative analysis, we first identify the analytical group for each cation:

1. Cu²⁺ (Copper ion): Belongs to Group II. The group reagent is H₂S gas in the presence of dilute HCl.
2. Al³⁺ (Aluminium ion): Belongs to Group III. The group reagent is NH₄OH in the presence of NH₄Cl.
3. Co²⁺ (Cobalt ion): Belongs to Group IV. The group reagent is H₂S gas in the presence of NH₄OH and NH₄Cl.
4. Ba²⁺ (Barium ion): Belongs to Group V. The group reagent is (NH₄)₂CO₃ in the presence of NH₄OH and NH₄Cl.
5. Mg²⁺ (Magnesium ion): Belongs to Group VI. The group reagent is (NH₄)₂HPO₄ in the presence of NH₄OH.

Now, we list the cations alongside their respective group numbers:
- B. Cu²⁺: Group II
- A. Al³⁺: Group III
- D. Co²⁺: Group IV
- C. Ba²⁺: Group V
- E. Mg²⁺: Group VI

Arranging these in increasing order of group numbers (from II to VI) gives us:
B (Group II) < A (Group III) < D (Group IV) < C (Group V) < E (Group VI)

Therefore, the correct sequence is B, A, D, C, E.