1s2,2s2,2p5(Z=9)The last electron is in the 2p-orbital, therefore it belongs to p-block elements.∴ Group number =10+7=17Period of the element =2nd⎡⎣⎢Number of the pricipal quantumvalence shell⎤⎦⎥Hence A=group17 and 2nd period.B. 1s2,2s22p6,3s23p6,4s2(Z=20)The last electron is in the 4s-orbital, therefore it belongs to s-block elements.∴ Group number =2 ( Number of electrons in the VALENCE shell)Period=4TH( Number of the PRINCIPAL quantum number of the valence shell)C. 1s2,2s22p6,3s2p6,4s1,3d10(Z=29)The last electron is in the 3d-orbital, therefore it belongs to d-block elements.∴ Group number =11th⎡⎣⎢⎢⎢⎢Number of electrons INTHE penultimate shellshell(i.e.in4s)=10+1=11⎤⎦⎥⎥⎥⎥Period=4th ( Number of the principle quantum number of the valence shell)D. =1s2,2s22p6,3s23p63s10,4s24p6(Z=36)The last electron is in the 4-p orbital ,therefore it belongs to p-block elements.∴ Group number =10+8=18Period =4th ( Number of the principle quantum number of the valence shell)E. =1s2,2s22p6,3s23p63d10,4s24p64d10,5s25p6,6s2,4f2(Z=58)The last electron is in the 4f-orbital, therefore it belongs to f-block elements.Note: The filling of 4f-orbitals OCCURS only when one electron has already entered 5d-orbital. Therefore, E belongs to f-blocks elements and not to d-block elements.Since it belongs to lanthanides series, therefore as such it does not have any group numberNote: But all lanthanides and actinides belong to group 3 (or IIIB).However, its period =6th⎡⎣⎢Number of hte principalquantum number ofthe valence shell⎤⎦⎥Related VideoExplanation: