# Can mass number of nucleus be equal to it's atomic number? [closed]

The mass number of a nucleus is

1. always less than its atomic number
2. always more than its atomic number
3. equal to its atomic number
4. sometimes more than and sometimes equal to its atomic number

I know that mass number is equal to the sum of number of protons and neutrons in the nucleus. And also number of protons are actually the atomic number of the elements. So I know that, why mass number is greater than atomic number. But I don't understand How can atomic number be equal to it's mass number. This means number of protons is equal to mass number i.e. number of neutrons is zero. And if there are no neutrons then how can it be called as nucleus? Is the given answer is wrong?

## closed as off-topic by FGSUZ, ZeroTheHero, Buzz, John Rennie, A.V.S.Feb 2 at 7:04

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Hydrogen atom $^1_1H$ i.e. an atom with one proton (and an electron) and no neutrons is the most abundant isotope in the universe. It has atomic number $Z=1$, and mass number $A=1$. Only in this case $A=Z$ since, as you said, a nucleus with more protons cannot be stable without neutrons.