If half life of a radioactive element is $3\, hours$, after $9\, hours$ its activity becomes
If half life of a radioactive element is $3\, hours$, after $9\, hours$ its activity becomes
- A
$1/9$
- B
$1/27$
- C
$1/6$
- D
$1/8$
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- [AIEEE 2012]
The half-life of $_{38}^{90} Sr$ is $28$ years. What is the disintegration rate of $15\; mg$ of this isotope?
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