Amino-acid substitute for tryptophan without altering proteins characteristics ?

Ans. is `b' i.e., Phenylalanine Tryptophan is an aromatic amino acid, thus it can only be replaced with other aromatic amino acid.Other two aromatic amino acids are :?PhenylalanineTyrosineAmong these two, phenylalanine can substitute tryptophan but not tyrosine becausePhenylalanine and tryptophan both are hydrophobic (non-polar).Whereas, tyrosine is hydrophilic (Polar)."The only other aromatic residue that can substitude for tryptophan is phenylalanine. Tyrosine cannot substitute since it has hydrophilic propey"