Rhizobium:

feed on legumes
add nitrogen to soil
are a special type of bacteria
all of the above

Is their a picture that goes along with it? ?

The proton has a positive charge while the neutron has no charge they both make up the nucleus of the atom while the elections have a negative charge and surround the nucleus of the atom. the protons and electrons are used to calculate the atom's mass whereas the neutrons don't affect the mass