Block — ব্লক
A block is one of the four table regions — s, p, d, f — named after the subshell receiving the last electron.
Definition
The periodic table splits into four blocks named after the subshell that accepts each element's final electron. The s block holds Groups 1 and 2 (plus helium): soft reactive metals with outer s electrons. The p block covers Groups 13 to 18, from boron across to noble gases. The d block, Groups 3 to 12, holds the transition metals filling inner d orbitals. The f block, placed below the main table, holds the lanthanides and actinides. Know the block and you can sketch the configuration at once.
For example
Sodium's last electron enters 3s, so it is an s-block metal; iron's land in 3d, making it a d-block transition metal; helium's sit in 1s, which is why this Group 18 oddball technically lives in the s block.