# Question #0ff3e

Sep 28, 2016

#### Answer:

$\text{2 days}$

#### Explanation:

A radioactive isotope's nuclear half-life tells you how much time must pass in order for half of the atoms present in a sample to undergo radioactive decay.

In your case, you start with $\text{10 g}$ of a radioactive substance. Two days after first interacting with the sample, you find that its mass decreased to $\text{5 g}$.

This is, of course, equivalent to saying that $\text{5 g}$ of the substance decayed. Since it took $2$ days for half of the sample to undergo radioactive decay, you can say that this radioactive isotope has a half-life of $2$ days.