What is an isotonic solution?
A. A solution whose concentration is lower than the internal concentration.
B. A solution whose concentration is the same as compared to internal concentration.
C. A solution whose water concentration is more than the internal concentration.
D. None of the above.

Hint: Isotonic is made from two words iso+tonic meaning same concentration of liquid. So, the isotonic solution refers to the solution having concentration equal inside and outside.

Complete answer:
> A solution whose concentration is lower than the internal concentration will be known as a hypotonic solution.
> A solution whose water concentration is the same as compared to internal concentration is known as isotonic solution.
> A solution whose water concentration is more than the internal concentration is known as hypertonic solution.

So, option B is the correct answer.

Additional Information: Isotonic solution contains an electrolytic balance similar to the plasma in the bloodstream. When an isotonic solution is poured, the fluid volume of the patient is increased. Common example of isotonic solution is 0.9% of saline and lactated ringers.

Note:
An isotonic solution is one that has the same concentration as another solution. If two solutions are separated by a semipermeable membrane, solution will flow in equal parts. As the concentration of solute and solvents are the same. This allows the free movement of ions, molecules across the membrane without disturbing concentration of solutes on either of sides. Isotonic solutions always have the same osmolarity, or solute concentration, as another solution. Ph balance has been maintained by my cells to create isotonic solutions.