Answer to Question #125260 in Atomic and Nuclear Physics for Asif Sultan

Question

How to solve it?
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Answer 1

We know, what do it means by half life, right?If not then it is defined as the requirement of time that need when the initial amounts of the radio active substance is exactly becomes half.

Now, in this case if you looked that initially amount of substance was 10gm which is scaled to 100 in the graph.Clearly , if you looked at vertical axis, you can find the number 50 which is half of 100 and follow the horizontal dashed line ,then immediately the vertical dashed line, you will get 3 hour which is half life.

Now, half life is 3 hour=180 min.

Clearly countdown will be $50\cdot180=9000$

Thus, correct option is A.