Step 1: Analyze the given vector relations.
Given that \( \mathbf{a} = \mathbf{c} \) and \( \mathbf{b} = \mathbf{a} \times \mathbf{c} \), we know that the cross product of two parallel vectors is zero. Hence, \( \mathbf{a} = 0 \) or \( \mathbf{b} = \mathbf{c} \).
Thus, the correct answer is (2).