The answer is protons. Neutrons have no charge and electrons have a negative charge so the positive charge must be protons.
The first blank can be filled with the Heliocentric model, and the second blank can be filled with Copernicus.
The heliocentric model known as heliocentrism was proposed by the Renaissance astronomer, mathematician, and the Catholic cleric Nicolaus Copernicus resulting in the Copernican revolution.
It is the astronomical model, in which the planets and the Earth revolve around the Sun positioned at the middle of the Solar system. Factually, the heliocentric model was in contrast to geocentrism, in which Earth is positioned at the center of the Solar system.
This is a lab assignment, you need to do something physically to find your answers
A0 = 1
a1 = 2
a2 = 1
a3 = 2
This can be solved by guessing and checking and making sure that all atoms on the left side are accounted for on the right side. Both sides must have the same amount of atoms or the balancing is not correct.