Step 1: Proteins are indeed polymers of $\alpha$-amino acids linked by peptide bonds (Assertion TRUE).

Step 2: However, a tetrapeptide (containing 4 amino acid residues) is formed by linking those 4 amino acids with only 3 peptide bonds, not 4 — each peptide bond forms between two consecutive amino acids, so n amino acids require (n−1) peptide bonds. The Reason's claim of '4 peptide bonds' for a tetrapeptide is FALSE.

Correct option: (d) Assertion (A) is false, but Reason (R) is true.

(Re-examining: since the Assertion is a correct, true general definition of proteins, and the Reason's specific numerical claim about a tetrapeptide is incorrect, the appropriate code is actually (c) Assertion (A) is true, but Reason (R) is false.)