Standard solution is one whose concentration is _______.

Options

A. decrmolar
B. exactly known
C. centrimolar
D. decinormal

Answer

To answer the question "Standard solution is one whose concentration is _______", we need to analyze the definition of a standard solution and the options provided.

### Step-by-Step Solution:

1. **Understanding Standard Solutions**: A standard solution is a solution that has a precisely known concentration of solute. This means that the amount of solute is accurately measured and the volume of the solution is also known.

2. **Analyzing the Options**: The options provided are:
- Decimolar
- Centimolar
- Exactly known
- Decinormal

3. **Defining the Terms**:
- **Decimolar**: This refers to a solution with a concentration of 0.1 M (1/10 M).
- **Centimolar**: This refers to a solution with a concentration of 0.01 M (1/100 M).
- **Decinormal**: This refers to a solution with a normality of 0.1 N (1/10 N).
- **Exactly known**: This term indicates that the concentration of the solution is precisely measured.

4. **Identifying the Correct Answer**: Among the options, the term that best describes a standard solution is "exactly known". This is because a standard solution is defined by its known concentration, which can be expressed in various units (molarity, normality, etc.), but the key characteristic is that the concentration is precisely known.

5. **Conclusion**: Therefore, the correct answer to the question is that a standard solution is one whose concentration is **exactly known**.

### Final Answer:
Standard solution is one whose concentration is **exactly known**.