[functions]

My instructor give me a question:
Mass number (number of protons and number of neutrons in an atom) is supposed to be a whole number for a particular atom, in reality IT IS NOT.  Why is it so? Here, I am very sure that this question ask for mass number (nucleon number) not atomic mass number.

[Borek]

Google mass deficit.

[sjb]

My instructor give me a question:
Mass number (number of protons and number of neutrons in an atom) is supposed to be a whole number for a particular atom, in reality IT IS NOT.  Why is it so? Here, I am very sure that this question ask for mass number (nucleon number) not atomic mass number.

Can you give some examples of where you have seen non-whole number mass numbers? As far as I know, this term means the same as atomic mass number, and is different to isotopic mass or relative atomic mass.

[functions]

My instructor give me a question:
Mass number (number of protons and number of neutrons in an atom) is supposed to be a whole number for a particular atom, in reality IT IS NOT.  Why is it so? Here, I am very sure that this question ask for mass number (nucleon number) not atomic mass number.

"Here, I am very sure that this question ask for mass number (nucleon number) not atomic mass number."
In the above sentence in my previous post there is a mistake, it should be atomic weight in place of atomic mass number.

[Borek]

(number of protons and number of neutrons in an atom) is supposed to be a whole number for a particular atom, in reality IT IS NOT.

This is false. For a given ATOM number of nucleons is an integer number.

However, atomic mass of an ELEMENT doesn't follow the same rule, as element is not necessarily composed of identical atoms.