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Select the correct option(s) regarding radioactivity of U²³⁵ and U3O8 (where all uranium is U²³⁵):

1. Specific activity of U²³⁵ is greater than specific activity of U3O8 (All 'U' is U²³⁵)
2. Activity of 1 mol U²³⁵ is greater than activity of 1 mol U3O8 (All 'U' is U²³⁵)
3. Decay constant of U²³⁵ is same whether it is pure U²³⁵ or U3O8 (All 'U' is U²³⁵)
4. Rate of radioactive disintegration increases with increase in temperature

Correct answer: Decay constant of U²³⁵ is same whether it is pure U²³⁵ or U3O8 (All 'U' is U²³⁵)

Solution

The decay constant is an intrinsic nuclear property and does not change with chemical environment or temperature — this statement is correct. Specific activity of U²³⁵ (pure) is higher than U3O8 because U3O8 has more mass per U atom (oxygen contributes mass but no radioactivity). For 1 mol: U3O8 contains 3 mol of U²³⁵ atoms, so its activity is 3 times that of 1 mol U²³⁵. Temperature has no effect on nuclear decay rates.

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