Question

why fulfilled and half-filled orbital are most stable . state hund's rules​

Answer 1

Answer:

Stability of Completely Filled and Half-filled Orbitals

This is because of two reasons: Symmetrical distribution: As everyone knows that symmetry leads to stability. The orbitals in which the sub-shell is exactly half-filled or completely filled are more stable because of the symmetrical distribution of electrons.

Answer 2

The exactly half-filled and fully filled orbitals have greater stability than other configurations. The reason for their stability are symmetry and exchange energy. The electrons present in the different orbitals of the same sub-shell can exchange their positions

also check the 1st attachment.

Hund's rule:

Every orbital in a subshell is singly occupied with one electron before any one orbital is doubly occupied and all electrons in singly occupied orbitals have the same spin.

The image (2) attached is the example of hund's rule.