if an atom has 17 protons, 18 neutrons, and 17 electrons, what is the mass of this atom?

The mass of this atom is 35 atomic mass units (amu). Here’s why: the mass of an atom (its mass number) is essentially the total number of protons plus neutrons in the nucleus. Protons and neutrons each contribute about 1 amu, while the mass of electrons is so small it is usually ignored at this level.

• Number of protons = 17
• Number of neutrons = 18
• Mass number = 17 + 18 = 35 amu

So, an atom with 17 protons, 18 neutrons, and 17 electrons has a mass of 35 amu.