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Assertion (Statement-1): Boron does not exhibit a +1 (univalent) oxidation state, whereas the +1 (unipositive) state of thallium is fairly stable. Reason (Statement-2): The inert pair effect is dominant in thallium. Select the correct option.

1. Statement-1 is true, Statement-2 is true and Statement-2 is the correct explanation of Statement-1.
2. Statement-1 is true, Statement-2 is true but Statement-2 is NOT the correct explanation of Statement-1.
3. Statement-1 is true, Statement-2 is false.
4. Statement-1 is false, Statement-2 is true.

Correct answer: Statement-1 is true, Statement-2 is true and Statement-2 is the correct explanation of Statement-1.

Solution

Boron is too small/light for inert-pair effect, so it only shows +3; in thallium the 6s electrons are held tightly (inert pair effect), making Tl(+1) the stable state. The reason correctly explains the assertion.

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