How old is a fossil bone whose C-14 content is 12.5 percent than that of living bone? Half-life of C-14 is 5.73 x 10³ years.

1. 25400 yr
2. 17190 yr
3. 22920 yr
4. 11460 yr
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Answer: B
Explanation:
• After three half-lives, the %age amount left behind = `100/2^3` = 12.5% . Thus total time period = 3 x 5730 = 17190 years.
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Iodine-131 has a half life of 8 days. In a 4.0 g sample of it, how many grams will remain after 24 days?

1. 1.0 g
2. 2.0 g
3. 0.5 g
4. 1.33 g
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Answer: C
Explanation:
• After 3 half-lives (8 x 3 = 24 days), the amount left will be = `(4g)/2^3=4/8` = 0.5 g.
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The half-life of Ca-45 is 146 days. What percentage of the original sample will remain after 1.0 year?

1. 17.68%
2. 10.90%
3. 12.50%
4. 25%
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Answer: A
Explanation:
• After 2.5 half-lives (1 year = 365 days, Half-lives = 365/146 = 2.5), the %age amount left behind = `100/2^2.5` = 17.68%
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Which of the followings equation can be used to calculate the amount of radioactive substance left after time t?

1. `log(N_o/N)=(lamda)/2.303t`
2. `log(N/N_o)=(lamdat)/2.303`
3. `log(N_o/N)=(lamdat)/2.303`
4. none of these
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Answer: C
Explanation:
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The statistical average of the lives of all the atoms present at any time is known as:

1. half-life
2. average life
3. Decaying time
4. radioactive dating
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Answer: B
Explanation:
• In a radioactive decay, some atoms decay earlier and other survive longer. The given statement is called average life.
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The average life is equal to the reciprocal of:

1. decay constant (λ)
2. half-life
3. number of radioactive atoms
4. none of these
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Answer: A
Explanation:
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Which expression relates the average life of a radioactive element to its half-life?

1. average life = 1.2 x half-life
2. half-life = average life x 1.4
3. average life = 1.44 x half-life
4. none of these
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Answer: C
Explanation:
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The average life is often used to express ---------- of a radioactive element:

1. half-life period
2. Decay time
3. radioactive dating
4. rate of disintegration
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Answer: D
Explanation:
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The average life of radium is:

1. 2500 years
2. 2400 years
3. 4200 years
4. 2000 years
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Answer: B
Explanation:
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Which of the following uranium isotope has the shortest half-life?

1. uranium-235
2. uranium-238
3. uranium-234
4. all have same half-lives
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Answer: C
Explanation:
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