NEETChemistryNuclear ChemistryMCQ+4 / −1
The half life of a first order reaction is 2000 years. If the concentration after 8000 years is 0.02 M, then the initial concentration was :
- A0.04 M
- B0.16 M
- C0.32 M
- D0.08 M
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Correct answer: C
Let the initial concentration is A molar.
Number of half lives in 8000 years $$ = {{8000} \over {2000}} = 4$$
$$0.02 = {{[A]} \over {{{(2)}^4}}}$$
$$[A] = 0.02 \times {2^4} = 0.32$$ M
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