Question

Red blood cells (RBCs) contain 0.9% NaCl in the intracellular fluid (ICF). What concentration of NaCl should the extracellular fluid (ECF) be to maintain an isotonic solution in which the cell does not shrink or burst?

Answer 1

Answer : 0.9% NaCl

When ICF and ECF have same osmotic concentration, they are said to be isotonic.
Here RBC contains 0.9% NaCl . In order to maintain isotonic solution with this, ECF should contain 0.9% NaCl.

If RBC placed in an isotonic solution, osmosis will not occur between ICF and ECF. RBC will neither shrink nor swell.

If RBC placed in 1% NaCl solution-- solution hypertonic--- water move from its higher concentration to its lower concentration (osmosis) --- RBC shrinks.

If RBC placed in 0.1% NaCl solution-- solution hypotonic--- water move from its higher concentration to its lower concentration --- RBC swells up.