An element with Z = 21  belongs to ………period of modern periodic table

detailed solution

Correct option is B

Hints to predict the position of element in the Modern periodic table :1)Elements from Z = 58-71……Lanthanoids…..4f series….6th period……3rd(IIIB) group;2)Elements from Z = 90-103……Actinoids…..5f series….7th period……3rd(IIIB) group;3)Elements from Z = 104-118………..Last two digits gives group number….. 7th period;4)Elements from Z = 31-57….subtract 18 to get preceding element;5)Elements from Z = 72-89….subtract 32 to get preceding element;6)Elements from Z = 104-120….subtract 32 to get preceding element ;For Z=104-120….simplest Hint7)Elements from Z = 104-120….subtract 82 to get a lower member(Z<30) belonging to same group;Hints 4, 5 and 6 can be used repeatedly until an element belonging to same group with Z < 30 is obtained;Elements with Z < 30 with their group, period and block can be known from Electronic configuration;Ex : Z=89, 57, 39, 21….belong to 3rd(IIIB) group;(n-1)d1-10ns1-2 ;Note : Many elements of d-block have anomalous configuration. So only GEC of each group is highlighted;(89-32)=57; (57-18)=39; (39-18)=21;Z = 21…….Sc…4s23d1….…n=4….4th period……d-block….…..3rd group;Z = 39…….Y….5s24d1….….n=5….5th period……d-block……...3rd group;Z = 57…….La…6s25d1…….n=6….6th period……d-block…..… 3rd group;Z = 89……..Ac..7s26d1…….n=7….7th period……d-block..……. 3rd group;