The atomic number of an element is 20. In modern periodic table, this element is placed:
(a) 2nd period
(b) 4th period
(c) 3rd period
(d) 1st period
(b) 4th period.
Electronic configuration : K L M N
2 8 8 2
Hence, from the electronic configuration, it is clear that the outermost electron goes into the 4th shell. So, the element would be placed in the 4th period.