An atom consist of electron, protons and neutrons. Protons and neutrons are present with in nucleus while the electrons are present out side the nucleus.
All these three subatomic particles construct an atom. A neutral atom have equal number of proton and electron. In other words we can say that negative and positive charges are equal in magnitude and cancel the each other. For example if neutral atom has 6 protons than it must have 6 electrons. The sum of neutrons and protons is the mass number of an atom while the number of protons are number of electrons is the atomic number of an atom.
For example
The number of protons and number of electrons in lead are 82 and it shows its atomic number. while the number of protons plus neutrons are mass number which is 207.2 amu.
He will likely succeed if only his nervousness is at the medium level for this will allow Vance to overcome his task as the medium level is set to overcome medium tasks in which he is on right now with lecturing in having to be nervous of doing or having a mistake.