$^{57}$ Co decays by electron capture.Its half-life is $272$ days. The activity left after a year is (if present activity is 2 $μ$ Ci)
$0.788 μ C i$
$0.431 μ C i$
$0.23 μ C i$
$0.39 μ C i$

0.788 μ C i

0.39 μ C i

0.431 μ C i

0.23 μ C i

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Solution

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Half life $= 272 d a y s$

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57Co decays by electron capture.Its half-life is 272 days. The activity left after a year is (if present activity is 2μCi)0.788μCi0.431μCi0.23μCi0.39μCi

Half life =272 days

$^{57}$ Co decays by electron capture.Its half-life is $272$ days. The activity left after a year is (if present activity is 2 $μ$ Ci)
$0.788 μ C i$
$0.431 μ C i$
$0.23 μ C i$
$0.39 μ C i$

Half life $= 272 d a y s$