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The disintegration rate of a certain radioactive sample at any instant is 4250 disintegrations per minute. 10 minutes later, the rate becomes 2250 disintegrations per minute. The approximate decay constant is (Take log 10 1.88 = 0.274)

1. 0.02 min –1
2. 2.7 min –1
3. 0.063 min –1
4. 6.3 min –1

Correct answer: 0.063 min –1

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