For electronic configuration =(n−1)d2ns2 Sum of electrons present in outer most orbital (d and s ) denoted group and period position is represented by principal quantum number. e.g. (n−1)d2ns2 Group = number of valence electrons in d and s-orbital. Sum of electrons in d and s orbital =2+2=4 ∴ Number of electrons in d-orbital and valence shell =4 ∴ 4th group and 4th period.