Question: 81. Given below are certain cations. Using inorganic qualitative analysis, arrange them in increasing group number from 0 to VI.
A. \mathrm{Al}^{3+}
B. \mathrm{Cu}^{2+}
C. \mathrm{Ba}^{2+}
D. \mathrm{Co}^{2+}
E. \mathrm{Mg}^{2+}
Choose the correct answer from the options given below:
(1) B, A, D, C, E
(2) \mathrm{B}, \mathrm{C}, \mathrm{A}, \mathrm{D}, \mathrm{E}
(3) \mathrm{E}, \mathrm{C}, \mathrm{D}, \mathrm{B}, \mathrm{A}
(4) \mathrm{E}, \mathrm{A}, \mathrm{B}, \mathrm{C}, \mathrm{D}
Answer: Option (1)
Explanation:
In inorganic qualitative analysis, cations are classified into groups based on the group reagent that precipitates them.
\mathrm{Cu}^{2+} belongs to Group II, as it forms insoluble sulfides with
\mathrm{H}_{2}\mathrm{S} in acidic medium.
\mathrm{Al}^{3+} belongs to Group III, as it precipitates as hydroxide with
\mathrm{NH}_{4}\mathrm{OH} in the presence of \mathrm{NH}_{4}\mathrm{Cl}.
\mathrm{Co}^{2+} belongs to Group IV, as it forms sulfide precipitates with
\mathrm{H}_{2}\mathrm{S} in alkaline medium.
\mathrm{Ba}^{2+} belongs to Group V, as it forms insoluble carbonates with
\mathrm{(NH}_{4})_{2}\mathrm{CO}_{3}.
\mathrm{Mg}^{2+} belongs to Group VI,
as it does not precipitate with common group reagents and is tested separately.
Therefore, the increasing order of group number from 0 to VI is
B, A, D, C, E.