Which of the following statements about hormones is incorrect?

Hormone insulin is released when there is rapid fall in blood glucose level.

The correct answer is Option (3) → Hormone insulin is released when there is rapid fall in blood glucose level.

Let us evaluate each statement about hormones to identify the incorrect one:

1. Hormones act as messengers between glands and receptors.

This statement is correct. Hormones are chemical messengers produced by glands in the endocrine system and are released into the bloodstream to communicate with various organs and tissues, facilitating regulatory functions.

2. Male sex hormones are used by athletes and sports persons to increase muscle strength.

This statement is correct. Athletes often misuse anabolic steroids (synthetic derivatives of male sex hormones) to enhance muscle mass and strength, which is against sports regulations.

3. Hormone insulin is released when there is rapid fall in blood glucose level.

This statement is incorrect. Insulin is actually released when blood glucose levels are high (e.g., after eating) to promote glucose uptake by cells and lower blood sugar levels. When there is a rapid fall in blood glucose, glucagon (another hormone) is released to increase blood sugar levels.

4. Abnormally low levels of thyroxine are characterized by obesity and lethargy.

This statement is correct. Low levels of thyroxine, a hormone produced by the thyroid gland, can lead to hypothyroidism, which is associated with symptoms like weight gain (obesity) and fatigue (lethargy).

Conclusion
The incorrect statement is: Hormone insulin is released when there is rapid fall in blood glucose level.