Radioactive plutonium-239 (t½ = 2.44 x 105 yr) is used in nuclear reactors and atomic bombs. If there are 4.4 x 102 g of the isotope in a small atomic bomb, how long will it take (in yr) for the substance to decay to 1.0 x 102 g, too small an amount for an effective bomb? This radioactive decay follows first order kinetics.

The time time taken for the sample to decay from to is

Explanation:

Expression for rate law for first order kinetics is given by:

where,

k = rate constant

t = age of sample

a = let initial amount of the reactant

a - x = amount left after decay process  

a) for completion of half life:

Half life is the amount of time taken by a radioactive material to decay to half of its original value.

b) time taken for the sample to decay from to

The time time taken for the sample to decay from to is

i think it's c. i'm not sure but i think so.