Which of the following illustrates the conservation of matter?
a. 4 al + 3 o2 —> 2 al2o3
b. 2 c2h6 + 6 o2 —> 4 co2 + 7 h2o
c. 4 co2 + h2 —> 2 ch4 + h2o
d. mg + o2 —> mgo

A. 4 Al + 3 O2 —> 2 Al2O3

Explanation:

4Al + 3O2 —> 2Al2O3

There are four aluminium and six oxygen atoms on both side of equation so this equation follow the law of conservation of matter.

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.

the correct answer is:

a. formation of precipitation