Which phrase best describes the time period in which the current body of scientific knowledge was developed?
a. just over the last 50 years
b. throughout all of history
c. mostly during roman times
d. mostly in the 20th century

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