List the cations which are capable of replacing aluminium in alums?

Explanation

To answer the question regarding the cations that can replace aluminum in alums, we need to first understand what alums are and the conditions under which certain cations can replace aluminum.

### Step-by-Step Solution:

1. **Understanding Alums**: Alums are double sulfates of the form M'2SO4·M''(SO4)2·12H2O, where M' is a monovalent cation (like potassium or sodium) and M'' is a trivalent cation (like aluminum).

2. **Identifying Cations**: The cations that can replace aluminum (Al³⁺) in alums must also be trivalent. This means we are looking for cations that have a +3 oxidation state.

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