Question

What is the increasing order of atomic sizes for the elements Li, Na, K?

• A. K < Li < Na
• B. Li < Na < K
• C. Li < K < Na
• D. Na < Li < K

Answer 1

The correct option is B Li < Na < K

• The atomic radius is the distance between the nucleus of an atom and its outermost orbit.
• The atomic numbers of Li, Na, K are 3, 11 and 19 respectively.

Element	Electronic Configuration
Lithium (Li)	2,1
Sodium (Na)	2,8,1
Potassium (K)	2,8,8,1

Since, a new shell gets added while going from lithium to potassium.
Hence, the size of the atom increases gradually in the order Li < Na < K.