Select all that apply: which of the following affect(s) the half-life of a radioactive substance?

a. the type of isotope
b. the temperature of the substance
c. the addition of a catalyst
d. the mass of the substance

The correct answer is option A, the type of isotope

Explanation:

The half life of a radioactive substance is a constant value and thus it is not affected by the temperature, catalyst or mass of the substance.  Basically it is the time taken by a radioactive substance to reduce its mass by half of its actual value. Radioactive decay takes place only when the atomic nucleus becomes unstable and thus the isotope type is the only factor which affects the radioactive decay of any element.  

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