The correct order of relative stability of half-filled and completely filled subshells is?

The correct option is C

As we know from our knowledge of atomic structure, if we are talking about the same principle quantum number, then p-orbitals are more stable than d orbitals.

But a completely filled d-orbital is more stable than a half-filled p-orbital because then it does not need more electrons to complete its orbital.

Hence, the correct order of relative stability of half-filled and completely filled sub-shell is $d^5<p^3<d^{10}<p^6$.