Final answer:
The first ionization of thallium produces the ion with the electron configuration [Xe] 5d10 6s1.
Step-by-step explanation:
The question asks which ionization of thallium produces an ion with the electron configuration [Xe] 5d106s1. The electron configuration of neutral thallium (Tl) is [Xe] 4f145d106s2. The first ionization removes one electron from the s-orbital, giving us [Xe] 4f145d106s1, which is the desired electron configuration. Therefore, the correct answer is a) First ionization.