Gas
Yes, hydrogen selenide is a gas at room temperature and pressure. It is a toxic and colorless gas with a foul odor.
Barium (Ba) and selenium (Se) can react to form barium selenide (BaSe), a compound that consists of barium cations and selenide anions. Barium selenide is typically a solid at room temperature and can be used in various applications, including electronics and as a semiconductor material. The reaction between barium and selenium involves the transfer of electrons, typical of metal and non-metal interactions.
Copper (I) Selenide by the stock system or Cupprous Selenide by the latin system.
lead (IV) selenide
A selenide contain the anion Se(2-).
titanium (II) selenide = SeTi
Thallium(III) Selenide
The systematic name of this ionic compound is Tin(IV) Selenide.
K2Se is potassium selenide or more precisely dipotassium selenide. As for KSe that probably doesn't exist, if it did it would be monopotassium selenide
The chemical formula for copper selenide is Cu2Se.
Hydrogen selenide is a polar compound.
The net charge of selenide is -2. Selenide is an anion that carries a charge of -2 due to the gain of two electrons in order to achieve a stable electron configuration.