Give the concentration of salt solution which is isotonic for R.B.Cs.

Answer

### Step-by-Step Solution:

1. **Understanding Isotonic Solutions**:
- An isotonic solution is one that has the same osmotic pressure as another solution, typically body fluids. In the case of red blood cells (RBCs), an isotonic solution will prevent the movement of water in and out of the cells.

2. **Identifying the Salt**:
- The salt commonly used to create isotonic solutions for RBCs is sodium chloride (NaCl).

3. **Normal Saline Concentration**:
- The standard isotonic solution for human blood is known as normal saline, which is a 0.9% solution of NaCl.

4. **Calculating the Concentration**:
- To prepare a 0.9% NaCl solution, you would dissolve 9 grams of NaCl in 1 liter of water. This concentration is isotonic with the osmolarity of blood plasma.

5. **Conclusion**:
- Therefore, the concentration of salt solution that is isotonic for RBCs is 0.9% NaCl.

### Final Answer:
The concentration of salt solution which is isotonic for RBCs is **0.9% NaCl**.

---