Explanation

The Supreme Court settled the constitutional standing of the Preamble across key rulings:

– In the Kesavananda Bharati case (1973) and reaffirmed in the LIC of India case (1995), the Supreme Court unequivocally ruled that the Preamble is an integral part of the Constitution.
– However, the Preamble is non-justiciable: it is neither a source of substantive legislative power for the government nor a source of constitutional prohibitions on legislative powers.
– It cannot be enforced independently in a court of law to invalidate a law; rather, it serves as an interpretive key to understand ambiguous constitutional provisions and statutes.

Hence, it is a part of the Constitution but has no legal effect independently of other parts — Option D.