Question

which statement about the half-life of a radioactive sample is true?
it is an exact measure of the decay of an individual atom
it measures the tendency of a radioisotope to decay radioactively
it is affected by the concentration of the radioactive substance that is present
it can be calculated based on neutron number

Explanation:

• Option 1: Half - life is a statistical measure for a large number of atoms, not for an individual atom. So this is false.
• Option 2: The half - life of a radioisotope is related to how likely (the tendency) it is to decay radioactively. A shorter half - life means a higher tendency to decay, and a longer half - life means a lower tendency. This statement is true.
• Option 3: The half - life of a radioactive substance is a characteristic property of the isotope and is not affected by the concentration (amount) of the radioactive substance present. So this is false.
• Option 4: Half - life is determined by the nuclear structure (proton - neutron ratio, etc.) of the isotope, but it is not calculated based on just the neutron number. So this is false.

Answer:

B. It measures the tendency of a radioisotope to decay radioactively (assuming the options are labeled A, B, C, D with the first option as A, second as B, etc. as per the order in the question)