Mg4S3 is not a recognized chemical compound, it does not exist according to the octet rule. According to the octet rule, a valid chemical compound between Magnesium and Sulfur would be MgS, in which Magnesium (Mg) and Sulfur (S) together form a balanced chemical bond. In MgS, Magnesium provides 2 electrons to Sulfur to form a stable electron configuration.
If we continue to assume that Mg4S3 exists, then we could say that this compound would consist of 4 atoms of magnesium and 3 atoms of sulfur. However, this cannot happen as sulfur can only form 2 chemical bonds without violating the octet rule.
Therefore, we cannot define the physical, chemical properties, chemical equations, or synthesis process for the compound Mg4S3 because it does not exist in reality.
However, understanding the octet rule is very important to know which chemical compounds can exist. The octet rule is a chemical rule that states atoms strive to configure their electrons to have 8 electrons in the outermost layer, creating the most stable electron configuration.