NPC is decidable

$NP Hard\preceq NPC$

So, NP Hard is atmost as hard as NPC

NP hard decidable

As, Undecidable is superset of decidable

NP Hard cannot be undecidable

$NP Hard\preceq NPC$

So, NP Hard is atmost as hard as NPC

NP hard decidable

As, Undecidable is superset of decidable

NP Hard cannot be undecidable