Answer:
A) the number of electrons in the outer shells.
Explanation:
The Bohr's model of the atoms shows that electrons orbits the nucleus in energy levels that are discrete and quantised. Orbital electrons are pulled by the nucleus. The nuclear pull is strongest on the shells closer to the nucleus and weakest as we reach the outermost sphere.
From this model, we see that chemical properties are governed by how much electrons an atom is ready to lose from its outermost shell in which the energy is the lowest. It is the electrons in the outermost shell or valence shell that determines how atoms would behave chemically.
The number of oxygen atoms = 3
Mass = 24 g
<h3>Further explanation</h3>
The formula of a compound shows the composition of the constituent elements
CaCO₃ is composed of 3 types of elements, namely Ca, C and O
The amounts of each of these elements in the compound CaCO₃:
So the number of oxygen atoms = 3
mass of Oxygen :

The area is 60.2, to find area it's length times width.