Here's why:

* Same group on the periodic table: Both sulfur and selenium belong to Group 16 (also called Chalcogens) on the periodic table. Elements in the same group share similar chemical properties.

* Similar electron configuration: They have the same number of valence electrons (electrons in the outermost shell), giving them similar bonding behavior.

* Similar oxidation states: Both can exhibit a variety of oxidation states, contributing to their similar chemical reactivity.

However, selenium is heavier than sulfur, meaning its properties will be slightly different. For example, selenium is less reactive than sulfur and has a higher melting point.