The correct answer is option 4 - Spleen. The spleen is not an excretory organ. It is a part of the lymphatic system and plays a role in filtering and storing blood, as well as producing and storing white blood cells.

Let`s now look at the other options to understand why they are or are not excretory organs.

Option 1 - Kidneys: The kidneys are indeed excretory organs. They filter waste products and excess water from the blood and produce urine.

Option 2 - Liver: The liver is not primarily an excretory organ, although it does play a role in removing toxins from the body. Its main functions include producing bile, metabolizing nutrients, and storing vitamins.

Option 3 - Lungs: The lungs are not excretory organs. They are primarily responsible for the exchange of gases, with carbon dioxide being exhaled as a waste product of respiration.

In conclusion, the spleen is the organ that is not involved in the excretory process.