Option 1: The National Commission for Backward Classes - The National Commission for Backward Classes (NCBC) is indeed a constitutional body in India. The Constitution of India under Article 338B (inserted through 102nd Constitutional Amendment) provides for the establishment of the National Commission for Backward Classes.

Option 2: The National Human Rights Commission - Though it's an important body, the National Human Rights Commission (NHRC) is not a constitutional body. It was established under Protection of Human Rights Act of 1993. It is actually a statutory body, so it’s not mentioned in the Constitution.

Option 3: The National Law Commission - There is no organization in India known as the National Law Commission. There is a body called the Law Commission of India but it is not a constitutional body. The Law Commission is established by an executive order and thus, it's a non-constitutional body.

Option 4: The National Consumer Disputes Redressal Commission - The National Consumer Disputes Redressal Commission (NCDRC) is also not a constitutional body. It was established under the Consumer Protection Act of 1986, so like the NHRC, it's a statutory body.

In conclusion of the above discussion, only one body out of the ones mentioned - The National Commission for Backward Classes - is a constitutional body.