How many neutrons are in an atom that has a mass number of 75 and contains 35 protons?

Question

I thought the answer was 40...was I wrong? If so, what is the correct answer and why?

Answer 1

I believe you are correct.  But chemistry class was 15 years ago for me.  I'm sure you could look up "atomic mass number" or similar on Wikipedia to find out for sure.

Answer 2

mass number = protons + neutrons

Therefore,

75 = 35 + neutrons.

So you're right: 40 is the correct answer.

Answer 3

Mass Number = Protons + Neutrons

75 = 35 + Neutrons

40 = Neutrons

You got the correct answer.

Answer 4

Yes, the correct answer is 40. The mass number is the sum of all protons and neutrons in the nucleus, collectively called nucleons.

75 - 35 = 40