The correct answer is D. a part of the Constitution but has no legal effect independently of other parts.

The Preamble of the Indian Constitution sets out the guiding principles and objectives of the document. While it is an integral part of the Constitution (Kesavananda Bharati case), it cannot be directly enforced in a court of law.

The Supreme Court of India has clarified that the Preamble can be used to interpret ambiguous provisions within the Constitution, but cannot be used to strike down laws as unconstitutional on its own. It serves as a guiding light for understanding the spirit and intent of the Constitution.