An unknown radioactive substance has a half-life of 3.20 hours . if 22.8 g of the substance is currently present, what mass a0 was present 8.00 hours ago? express your answer with the appropriate units.

129 g

Explanation:

The radioactive decay of a substance can be represented through the following expression.

where,

A is the amount of A at certain time t

A₀ is the initial amount of A

k is the rate constant

We can find k from the half-life (t1/2) using the following expression.

If 22.8 g of the substance is currently present, what mass A₀ was present 8.00 hours ago?

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i believe the answer is a.