Question

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

Answer 1

(b) 4^th 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 4^th shell. So, the element would be placed in the 4^th period.