What is the valency of selenium in five membered ring system?

More than likely it will be 4 or 6 but there is no way of knowing without knowing the system.

Thank you Sir, but if it is five membered ring system having 1-Se, 2-N, 3-C=O, 4-CH2, 5-CH2 then what will be the valency of Se in this type of ring system?

To determine the valency of selenium in a five-membered ring system, you need to understand the concept of valency and the structure of the ring system.

Valency refers to the combining capacity of an element, which is determined by the number of electrons it can gain, lose, or share to form chemical bonds. In the case of selenium, its valency can vary depending on the specific chemical environment.

To determine the valency of selenium in a five-membered ring system, you need to examine the structure of the ring and identify the oxidation state or formal charge of selenium.

If you have a specific five-membered ring system in mind, please provide additional details about the structure or the specific compound containing selenium. With more information, I can help you determine the valency more accurately.