If a rock sample has a half-life of 10 years, and has 100 atoms of parent materi today, how many half-lives will have passed before it has only 25 atoms of parent material left Explain your reasoning

2

Explanation:

The half-life of a radioactive material is the time taken for a nuclide to decay to half its original composition.

Given:

 Half-life  = 10yrs

  Number of atoms in parent  = 100atoms

Unknown:

Number of half-lives what will pass for 25 atoms to remain:

                                     Start                         First half life     Second half life

Number of years           0                                    10                       20

Number of atoms          100                                 50                      25

The number of half-lives that will pass is 2

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