Which definition describes a half-life?

the time required for half of a radioactive sample to decay.

the time required for half of a radioactive sample to become unstable.

the time required for all of a radioactive sample to change because of heat.

the time required for all of a sample to break down due to pressure change.

Half life can be defined as the time taken by a radioactive nuclei to decay into half of its original value.

If [A]₀ and [A] are the initial concentration and that after time 't' of a certain radioisotope, then the ratio of the concentrations is related to the rate of decay k, as follows:

[A]/[A]₀ = exp[-kt]

now, the rate constant k is related to the half life t1/2 as:

t1/2 = 0.693/k

Ans: (a) The time required for half of a radioactive sample to decay

b. atoms in metallic solids are not arranged in a regular pattern

explanation: