Casein, the milk protein is: (A) Nucleoprotein, (B) Chromoprotein, (C) Phosphoprotein, (D) Glycoprotein
Answer is C. Phosphoproteins: These contain phosphorus. Casein of milk and vitellin of egg yolk are examples. The phosphoric acid is esterified to the hydroxyl groups of serine and threonine residues of proteins.
Reference: Vasudevan 7th  ed, pg 43