How do you determine the number of protons in the nucleus?
Look at the atomic number on the periodic table
How can scientists determine whether the nucleus formed is that of a new element or that of isotope of a known element?
They can tell whether the nucleus formed is that of a new element or that of an isotope by determining the number of protons inside the nucleus. If the number of protons are different, then it is a different element (not necessarily new). If the number of protons are the same, then it is an isotope.
The number of protons in a nucleus depends on which element it is. ( The number of protons is the decider as to which element it is. ) The number of electrons in an atom is the same as the number of protons in the nucleus, but none of the electrons are in the nucleus. Rather, they orbit around the nucleus like planets round a star.