Consider the hypothetical situation where the azimuthal quantum number, l, takes values 0,1,2, ………… n+1, where n is the principal quantum number. Then, the element with atomic number

‘l’ can have values (n-1) to (n+1) total n+2 energy levels1 s1p1 d 2 s2p2 d2f         1) Atomic number 18 is having electronic configuration  1s21p61d10 and is noble gas.          2) Atomic number ‘19’ is first alkali metal          3) Atomic number ‘6’ has  1s, 1p valence subshell.          4) atomic number 16 has 1s21p61d5  halffilled d-configuration