What determines an atoms chemical properties?

The letter A is the right answer.

Explanation:

The Valencian Layer is the last electron distribution layer of an atom. The number of electrons present in this layer is what determines the chemical properties of an atom. According to the Octet Rule, the valence shell needs eight electrons to stabilize. Thus, atoms acquire stability when they have 8 electrons in the valence shell. This happens with noble gases, they have the full valence layer. The only exception is the Helium element that has 2 electrons. The other elements must make chemical bonds to receive the missing electrons and reach the eight electrons in the valence shell.

The electrons in the valence shell are the ones that participate in the bonds, because they are the most external ones.

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