Question

What is the position of the element in the periodic table satisfying the electronic configuration (n – 1)d¹ns² for n = 4?

Answer 1

(n - 1)d¹ ns²

For n = 4

= (4 - 1)d¹ 4s²

= 3d¹ 4s²

Now if we write it in the order of filling the sub shells, we know that first 4s fill then 3d fill so

4s² 3d¹

Now

period = Highest principal quantum number = 4th period

Group = 1 + 2 = 2 group

And the Atomic number is 21

Hope this helps you..