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A radioactive sample with a half-life of 1 month has the label : 'Activity = 2 microcurie on 1-8-1991'. What would be its activity two months earlier ?

Asked in CBSE AIPMT 1988 · Activity and decay constant

• (1) 1.0 microcurie
• (2) 0.5 microcurie
• (3) 4 microcurie
• (4) 8 microcurie

Step-by-step solution

Why the other options are wrong

• (1) comes from halves the activity once, stepping forward in time instead of back.
• (2) comes from halves it twice, giving the activity two months later rather than two months earlier.
• (3) comes from doubles only once, counting one month instead of two.

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