Question

Define half-life and mean life of a
radioactive nucleus. State the relation
between them.
​

Answer 1

half life

it is time interval in which the mass of a radioactive substance ,or the no. of its aton is reduced to half from its initial value is called the half life of substance

Answer 2

half life of a radioactive element is defined as the amount of time taken by an radioactive substance to decay itself to half of its initial concentration (example: if u have 100 kg of a radioactive substance then time taken by it to decay itself to 50 kg is called as half life of that radioactive substance)

mean life is defined as reciprocal of half life

T(1/2)=1/Ta

where T(1/2)=half life

Ta=mean life

T(1/2)=0.693Ta

hope this helps and u understand well :)