The answer is 1250 grams of substance will be left after 42 days.
What is Half Life ?
Half-life time is the time needed for the reactants to be in its half concentration.
It is known that the decay of a radioactive isotope obeys first order kinetics.
Also, it is clear that in first order decay the half-life time is independent of the initial concentration.
If reactant has initial concentration [A₀],
after half-life time its concentration will be ([A₀]/2).
The half-life time of the substance = 14 days.
42 days means 3 half life
After 1 half life the substance left is
= 10000/2
= 5000 grams
After second Half Life
=5000/2
=2500 grams
After Third Half Life
=2500/2
=1250 grams
Therefore 1250 grams of substance will be left after 42 days.
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