Topic: Interchange of Parts of Speech,

Best Answer Explained in Below-:

The correct noun form of the verb "solve" is "solution," which reflects the act of resolving a problem or the outcome of that action. In grammatical terms, many verbs have associated nouns that denote the result or process related to the action.

1. **Solution**: This noun directly pertains to the result of solving a problem, making it the most straightforward answer. In mathematics, chemistry, and everyday problem-solving, a "solution" indicates the answer or the method used to arrive at that answer.

2. **Solved**: This option is the past tense of the verb and indicates that an action has already been completed, but it does not serve as a noun itself.

3. **Solveness**: This is not a widely recognized term in English and does not relate directly to the verb "solve."

4. **Solvent**: While it is a legitimate noun, referring to a substance in which other substances dissolve, it is not specifically tied to the concept of solving problems or answers.

Therefore, "solution" is the most appropriate noun form linked to "solve," representing both the action of solving and the outcome of that action.