Question

Blood has been found to be isotonic with:
(a)-Normal saline solution
(b)- Saturated NaCl solution.
(c)- Saturated KCl solution.
(d)- A saturated solution of a 1:1 mixture of NaCl and KCl.

Answer 1

Isotonic solutions are those which have the same osmotic pressure. The concentration of the solution is observed for finding isotonic solutions.

Complete answer:
Let us first understand the isotonic solution:
The osmotic pressure is calculated with,

$\pi =CRT$

Where $\pi$ is the osmotic pressure, C is the concentration, R is the solution constant and T is the temperature.
So, from the above equation, it is evident that if two solutions have the values of C and T, they must have the same value of $\pi$. We can also say, solutions of equimolar concentration at the same temperature must have the same osmotic pressure.
The solutions which have the same osmotic pressure at the same temperature are called an isotonic solution.
The salt concentration in blood plasma due to different species present in it is equivalent to 0.9% aqueous solution of NaCl (mass/volume). Hence, we can say that:
A 0.9% solution of pure NaCl is isotonic with human red blood cells (RBC). Therefore, in this solution, RBC neither will swell nor undergo plasmolysis.
A pure NaCl solution with a concentration of less than 0.9% is called a hypotonic solution. On placing RBC in the solution, they will swell and even burst.
A pure NaCl solution with a concentration of more than 0.9% is called a hypertonic solution. On placing RBC in the solution, they will swell shrink due to plasmolysis.

So, the correct answer is “Option A”.

Note: We can also see that option (b), (c), and (d) all the solutions are saturated, which means they have high solute content and are very concentrated solutions. Hence, all of them will act as a hypertonic solution.