How Much How Fast & How Far E.2 Rate of Chemical Change (id: dd2c71582)

本题目来源于试卷: How Much How Fast & How Far E.2 Rate of Chemical Change，类别为 IB化学

[单选题]

Cesium-137 has a half-life of 30 years, and its decay is first order.

How long will it take for a 400 g sample to be reduced to 25 g?

A. 90 years
B. 30 years
C. 60 years
D. 120 years


参考答案:  D


本题详细解析:

D

Reducing the sample from 400 $�$ to 25 $�$ would take 4 half-lives, $4\times 30=120$ years.

400 $�$ $\stackrel{1}{\to }$ 200 $�$ $\stackrel{2}{\to }$ 100 $�$ $\stackrel{3}{\to }$ 50 $�$ $\stackrel{4}{\to }$ 25 $�$

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