Question

Which is not true for arginine?

• A. It is a crystalline solid.
• B. It has high solubility in benzene.
• C. It has a fairly high melting point.
• D. It is associated with more than one \(pk_a\) values.

Hint:

Amino acids are soluble in polar solvents due to their zwitterionic nature.

Answer 1

The Correct Option is B

To determine which statement about arginine is not true, let's evaluate each option:

1. It is a crystalline solid.
   Arginine is indeed a crystalline solid at room temperature. It is commonly found in amino acid form, which typically crystallizes.
2. It has high solubility in benzene.
   This statement is not true. Arginine is a polar amino acid due to the presence of its guanidinium group, and it is not soluble in non-polar solvents like benzene. This property makes option B the correct choice as the statement that is not true for arginine.
3. It has a fairly high melting point.
   Arginine has a high melting point, typically above 200°C, which is consistent with solid amino acids that form stable internal hydrogen bonds.
4. It is associated with more than one \(pK_a\) values.
   This is true as well since arginine has multiple ionizable groups (an α-amino group, a carboxyl group, and a guanidinium side chain), conferring more than one \(pK_a\) value.

Based on the evaluation, the statement "It has high solubility in benzene." is incorrect regarding the chemical properties of arginine. Therefore, option B is the correct answer.