The law of conservation of matter states that matter can be neither created nor destroyed. Your friend shows you the following chemical equation:
CaCO3+CaO+CO,
He says that because the oxygen atoms are split iretween two different molecules in
the products, the equation does not support the law of conservation of matter. Is
your friend right? Explain your answer.

The equation you wrote is incorrect,

the correct is: CaCO3+CaO+CO2

The law of conservation of mass or principle of mass conservation states that for any system closed to all transfers of matter and energy, the mass of the system must remain constant over time, as the system's mass cannot change, so quantity can neither be added nor be removed. Therefore, the quantity of mass is conserved over time.

Your friend is incorrect in saying that this doesn't follow the law of conservation of mass. The molecule of oxygen is split up but the number of total atoms of oxygen is same. So, it follows the law of conservation of mass.

potential energy is directly proportional to height.

more height = more potential energy.

greatest increase in height = greatest increase in potential energy

where are the points with the greatest increase in height ?

has to be c-e or d-e .