Question

A 60-gram sample of radioactive isotope is measured after two half-lives have passed. What pair of percentages describe the sample after two-half lives? A.) 50% unchanged and 50% stable B.) 25% unchanged and 75% stable C.) 12.5% unchanged and 87.5% stable D.) 75% unchanged and 25% stable

Answer 1

B. 25% unchanged and 75% stable

Step-by-step explanation:

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Answer 2

Answer: B.) 25% unchanged and 75% stable

Explanation:

Now, to calculate the initial amount of radioactive isotope

`a=(a_o)/(2^n)`

where,

a = amount of reactant left after n-half lives = 60 g

`a_o` = Initial amount of the reactant = ?

n = number of half lives= 2

Putting values in above equation, we get:

`60=(a^0)/(2^2)`

`a_0=240g`

Thus percentage of sample unchanged=
`(60)/(240)* 100\%=25\%`

The percentage of sample decayed or has become stable=
`(180)/(240)* 100\%= 75\%`