Question

1/32nd of a radioactive element's atoms remain in a lunar rock sample. How many half lives old is the rock?

A. 1

B. 2

C. 3

D. 4

E. 5

Answer 1

Answer:

E. 5

Explanation:

N₀ = initial total number of radioactive elements number

N = Number of atoms of radioactive element after "n" half lives = N₀ /32

n = number of half lives

Number of atoms of radioactive element after "n" half lives is given as

$N = N_{o}\left ( \frac{1}{2} \right )^{n}$

inserting the values

$\frac{N_{0}}{32} = N_{o}\left ( \frac{1}{2} \right )^{n}$

$\frac{1}{32} = \left ( \frac{1}{2} \right )^{n}$

n = 5