An element has an atomic number of 8 and a mass number of 16. How many neutrons does this element have?

An element with an atomic number of 8 and a mass number of 16 has 8 neutrons.

Let's break down the information to understand why.

The atomic number of an element tells you the number of protons in its nucleus. In this case, the element has an atomic number of 8, which means it has 8 protons.

The mass number of an element is the sum of its protons and neutrons. In this case, the mass number is 16.

To calculate the number of neutrons, we subtract the atomic number from the mass number: Number of Neutrons = Mass Number - Atomic Number

So, in this case, the number of neutrons would be: 16 (mass number) - 8 (atomic number) = 8 neutrons.

Therefore, the element in question has 8 neutrons.