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Question
Account for the following observations:
The +1 oxidation state of thallium is more stable than its +3 state.
Solution
As we move down the group in group 13 the participation of s-electrons in bond formation decreases the primary reason behind this is the inert pair effect. In this the p-electrons take part in bond formation and more energy is required to unpair the valence electrons to make them participate in bonding. Due to this the lower oxidation state of elements becomes stable than the higher oxidation state. As for thallium, +1 oxidation state is more stable than +3.
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