Replace with new samples of the powders and repeat, this time adding drops of the base. record observations in the table.
what do they mean

What they mean by "base" is the substance. A base is a substance that tastes bitter, has a pH that is greater than 7. It also turns red litmus paper blue. 

In conclusion, what they mean by 'base' is the substance included. 

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