Answer:
The acid in the lemon juice denatured the milk proteins.
Explanation:
The important biomolecule of the living organism is protein. Proteins are made of the repeating units of the alpha amino acids that are attached together through the peptide bond.
The proteins get denatured if they are subjected to the change in the temperature conditions or the additions of the chemicals. The addition of the lemon juice that acts as the acid coagulates the protein present in the milk and results in the clump formation.
Thus, the correct answer is option (a).