The correct answer is Only one.

Explanation: Out of the given organizations/bodies, only the National Commission for Backward Classes is a constitutional body. It was given constitutional status by the 102nd Constitutional Amendment Act, 2018, under Article 338B.

• The National Human Rights Commission is a statutory body, established by the Protection of Human Rights Act, 1993.
• The National Law Commission is also a non-constitutional, statutory advisory body.
• The National Consumer Disputes Redressal Commission is a quasi-judicial body set up under the Consumer Protection Act, 1986.

Thus, only one of the listed bodies is a constitutional body.