I have two questions:
It's said that in p block there's gradation in physical and chemical properties of elements. What is meant by this statement?
Why are the different blocks named s, p, d and f?
'p' block elements contain both metal and non-metal and we observe a gradation of properties (such as electropositivity, electronegativity, reducing or oxidising property etc.) as we move from left to right in a period.
From the Wikipedia article on atomic orbital:
They are derived from the description by early spectroscopists of certain series of alkali metal spectroscopic lines as sharp, principal, diffuse, and fundamental. Orbitals for ℓ > 3 continue alphabetically, omitting j (g, h, i, k, …)