Question

Electrons in.......... shell are called valence electrons.

Answer 1

Electrons in valence shell are called valence electrons. For example, electronic configuration of calcium is : $Ca$ : ${1s}^2$ ${2s}^2$ $2p^6$ $3s^2$ $3p^6$ $4s^2$. Here, valence shell of calcium is $4s$ and it has $2$ electrons in it. Therefore, $Ca$ has $2$ valence electrons. Hence, valence electron is an outer shell electron that is associated with an atom, that can participate in formation of a chemical bond.