Which of the following cations cannot be detected by the borax bead or microcosmic bead test? — Qualitative and Quantitative Analysis Chemistry Question

💡 Solution & Explanation

Step 1: The combination of NH4Cl and NH4OH is the group reagent for analytical Group III. Step 2: It is designed to selectively precipitate Group III cations (such as Al3+) as hydroxides by using the common ion effect of NH4+ to keep the OH- concentration too low to precipitate Group IV (Ni2+) or Group V/VI (Mg2+) cations. Step 3: Therefore, only Al3+ precipitates as Al(OH)3, while Ni2+ and Mg2+ remain in solution, matching option (a).