You can find the information about the number of neutrons, electrons, and protons in the atom in the periodic table of elements.
In the periodic table, the elements are arranged in the order of their atomic number A, usually located on the upper left side of the element symbol. This is the number of protons, the positively charged particles in the nucleus of an atom. In a non-ionic atom, this is also the number of electrons, the negatively charged particles, orbiting around the nucleus according to the planetary model of an atom.
The mass number of the element, Z, is usually found on the bottom left side of the element symbol, and equals the total number of particles inside the nucleus, proton and neutrons. This number might not be an integer because different isotopes of the same elements have different number of neutrons, and the mass number represents the average mass, usually very close to the mass of the most common isotope.
The electrons are much lighter than either protons and neutrons, so their mass is considered negligible compared to the mass of the nucleus.
Since the atomic number A is the number of protons, and the mass number Z is the total number of protons and neutrons, the number of neutrons N can be calculated as
N = Z - A,
by subtracting the atomic number from the mass number.