1. The half-life of Co-60 is 5.3 years. If the initial mass of the sample is 1000g, how much will remain after 15.9 years.

125 g

Explanation:

The following data were obtained from the question:

Half-life (t½) = 5.3 years.

Original amount (N₀) = 1000 g

Time (t) = 15.9 years.

Amount remaining (N) =?

Next, we shall determine the number of half-lives that has elapsed. This can be obtained as follow:

Half-life (t½) = 5.3 years.

Time (t) = 15.9 years.

Number of half-lives (n) =?

n = t / t½

n = 15.9 / 5.3

n = 3

Thus, 3 half-lives has elapsed.

Finally, we shall determine the amount of Co–60 that is remaining. This can be obtained as follow:

Original amount (N₀) = 1000 g

Number of half-lives (n) = 3

Amount remaining (N) =?

N = 1/2ⁿ × N₀

N = 1/2³ × 1000

N = 1/8 × 1000

N = 0.125 × 1000

N = 125 g

Therefore, the amount of Co–60 that is remaining is 125 g

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