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Select the correct formula for the compound formed from potassium and selenium

a. KSe

b. K2Se

c. KSe2

d. K2Se3

e. K3Se2

Solution: Potassium is a metal and selenium is a nonmetal, making the compound ionic. To write the formula for ionic compounds, we first figure out the oxidation numbers and then cross multiply them. Potassium is in Group1 on the Periodic Table and has an oxidation number of +1. Selenium is in Group 16 and has an oxidation number of -2.

K+1 Se-2, we need to exchange the numbers to get K2Se1 or K2Se.

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