In a balanced chemical equation,
select one:
a. coefficients are equal
b. energy is not conserved
c. atoms are conserved
d. molecules are equal

C) atoms are conserved.

Explanation:

In balanced chemical equation number of atoms are always conserved.

4KI + 2CuCl₂  →   2CuI  + I₂  + 4KCl

We can see there are four potassium, four iodine, two copper and four chlorine atoms are present on both side of equation. Which means atoms are conserved.

The balance chemical equation hold the law of conservation of mass.

Law of conservation of mass:

According to the law of conservation mass, mass can neither be created nor destroyed in a chemical equation.

Explanation:

This law was given by french chemist  Antoine Lavoisier in 1789. According to this law mass of reactant and mass of product must be equal, because masses are not created or destroyed in a chemical reaction.

For example:

In given photosynthesis reaction:

6CO₂ + 6H₂O + energy → C₆H₁₂O₆ + 6O₂

there are six carbon atoms, eighteen oxygen atoms and twelve hydrogen atoms on the both side of equation so this reaction followed the law of conservation of mass.

Other options:

a) Coefficients are equal.

While the coefficient with reactant and product can be different.

d) Molecules are equal

The number of Molecules can be different in balanced chemical equation

b) Energy is not conserved.

Energy can not be created or destroyed it remain unchanged.

your answer is a. the enthalpy of formation for a pure element in its standard state is always positive.