Isotonic solutions have same

Options

A. Molar concentration
B. Molality
C. Normality
D. None of these

Explanation

To determine what isotonic solutions have in common, we can analyze the concept of osmotic pressure and its relationship with concentration.

### Step-by-Step Solution:

1. **Understanding Isotonic Solutions**:
- Isotonic solutions are solutions that have the same osmotic pressure. This means that when two solutions are separated by a semipermeable membrane, there will be no net movement of solvent molecules between them.

2. **Osmotic Pressure Formula**:
- The osmotic pressure (π) of a solution can be calculated using the formula:
\[ \pi = CRT \]
where:
- \( \pi \) = osmotic pressure
- \( C \) = concentration of the solution (molarity)
- \( R \) = universal gas constant
- \( T \) = temperature in Kelvin

3. **Setting Up the Equation**:
- For two solutions to be isotonic, their osmotic pressures must be equal:
\[ \pi_1 = \pi_2 \]
- Substituting the osmotic pressure formula for both solutions gives:
\[ C_1RT = C_2RT \]

4. **Simplifying the Equation**:
- Since \( R \) (gas constant) and \( T \) (temperature) are the same for both solutions, we can cancel them out:
\[ C_1 = C_2 \]

5. **Conclusion**:
- The concentrations \( C_1 \) and \( C_2 \) must be equal for the two solutions to be isotonic. Since concentration is often expressed in terms of molarity, we conclude that isotonic solutions have the same molarity.

### Final Answer:
Isotonic solutions have the same **molarity** (or molar concentration).

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