## Answer :

**Answer:**

**10**

**Explanation:**

An isotope's **half-life** is the amount of **time **it takes for **half **of the **isotope's mass** to **decay**.

The isotope has a half-life of 24 hours, or 1 day. 1 week is equal to 7 days, so the isotope will undergo 7 half-lives. The number of nuclei remaining after being halved 7 times is:

n = 1280 (½)⁷

n = 10