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The amount of time it takes for half of a sample to disappear is:

a
nuclear chemistry
b
fission
c
fusion
d
half-life
Question 15
Video #5, Question #2

The half-life for a 100-gram sample of radioactive element X is 5 days. How much of element X remains after 10 days have passed?

a
50 g
b
100 g
c
25 g
d
75 g
Question 16
Video #5, Question #3

Sodium-24 has a half-life of approximately 15 hours. If only one-eighth of the sodium-24 remains, about how much time has passed?

a
30 hours
b
45 hours
c
60 hours
d
15 hours

1 answer

Here are the answers to your questions:

Question 14: The amount of time it takes for half of a sample to disappear is:

  • Answer: d) half-life

Question 15: The half-life for a 100-gram sample of radioactive element X is 5 days. How much of element X remains after 10 days have passed?

  • After 5 days, 50 grams will remain (half of 100 grams).
  • After another 5 days (10 days total), half of 50 grams remains, which is 25 grams.
  • Answer: c) 25 g

Question 16: Sodium-24 has a half-life of approximately 15 hours. If only one-eighth of the sodium-24 remains, about how much time has passed?

  • One-eighth of the original amount means that three half-lives have passed, since:
    • After 1 half-life: 1/2 remains
    • After 2 half-lives: 1/4 remains
    • After 3 half-lives: 1/8 remains
  • Since each half-life is 15 hours, the total time is 3 * 15 hours = 45 hours.
  • Answer: b) 45 hours