Step 1: Source of description.
The 42nd Amendment (1976) inserted the word {``Secular''} into the Preamble, explicitly describing India’s state character.
Step 2: Evaluate alternatives.
FRs ensure religious freedoms; DPSPs guide state policy; the 9th Schedule lists certain laws—none {describe} India as ``secular'' explicitly.
Step 3: Conclude.
\[
\boxed{\text{Preamble (Option B).}}
\]