Answer:

Blood cells, including red blood cells, are a vital component of our circulatory system. They are responsible for transporting oxygen and nutrients to various tissues and organs in the body. The shape and integrity of blood cells are crucial for their proper functioning.

Explanation:

The question asks about the condition in which blood cells retain their normal shape in a solution. Let's examine the different options and understand their effects on blood cells:

A) Hypotonic to blood:
A hypotonic solution has a lower concentration of solutes compared to the blood cells. When blood cells are placed in a hypotonic solution, water molecules move into the cells through osmosis. This causes the cells to swell and potentially burst, leading to a change in their shape. Therefore, blood cells do not retain their normal shape in a hypotonic solution.

B) Isotonic to blood:
An isotonic solution has the same concentration of solutes as the blood cells. When blood cells are placed in an isotonic solution, there is no net movement of water molecules. As a result, blood cells neither shrink nor swell, and they retain their normal shape. This is the correct option.

C) Hypertonic to blood:
A hypertonic solution has a higher concentration of solutes compared to the blood cells. When blood cells are placed in a hypertonic solution, water molecules move out of the cells through osmosis. This causes the cells to shrink and lose their normal shape. Therefore, blood cells do not retain their normal shape in a hypertonic solution.

D) Equinormal to blood:
The term "equinormal" is not a commonly used scientific term in this context. It is likely a distractor option that does not accurately describe the relationship between the solution and blood cells.

In conclusion, blood cells retain their normal shape in an isotonic solution, where the concentration of solutes is the same as that of blood cells.