Some nitrogen atoms have seven neutrons and some have eight neutrons these two forms of nitrogen are

They're the Isotopes of nitrogen atoms.

the atoms of the same kind of element, which has a same number of protons but a different number of neutrons, they're referred as the Isotopes of the element.

Not all elements has Isotopes, and each element's Isotopes are different. Some may be unstable, some may be stable.

Isotopes of the element must have the same number of protons, as proton is never changed in an element, it's like an ID number. Only the number of neutron is different, and not the electron numbers too, or else it'll become an ion. When we talk about Isotopes of an element, we usually say it in form of the element name, then followed by the mass number (proton + neutron), therefore, for example in the question, nitrogen has a proton number of 7, so the isotope with 7 neutrons is regarded as nitrogen-14.

Ithink it’s 3 as the answer.