Answer:
D. Valence electrons
Explanation;
An atom consist of electron, protons and neutrons. Protons and neutrons are present with in nucleus while the electrons are present out side the nucleus. All these three subatomic particles construct an atom.
When an atom chemically react with another atom bonds are formed. During this reaction valance electrons take part in chemical reaction or bonding.
Valance electrons are those electrons which are present in valance shell. While inner shell electrons are not involve in bonding these are called core electrons.
For example:
Consider the reaction between sodium and chlorine. In sodium there are two electrons in 1st energy level eight electrons in second energy level and one electron in outer most energy level which is valance electron. while chlorine has seven valance electron. Sodium lose its outer most or valance electron which is accepted by chlorine and ionic bond is formed.
Na + Cl → NaCl
