Final answer:
The real estate tax lien is valid without formal recording, unlike mechanic's, judgment, and mortgage liens, which require recording.
Step-by-step explanation:
The lien that does not need to be recorded to be valid is C) Real estate tax lien. A real estate tax lien is automatically placed on property by statute when taxes assessed on the property remain unpaid. It does not require formal recording to have validity. In contrast, a mechanic's lien, judgment lien, and mortgage lien typically require recording with a county recorder or similar local government entity to provide public notice and be enforceable against third parties.