In the 19th century, dmitri mendeleev predicted the existent of a then unknown element, x, with a mass of 68. he also predicted that an oxide of x would have the formula x2o3, on the modern period table. what is the group number and period of the element?

Base on your question that in 19th century when Dmitri Mendeleev predicted the existent of an unknown element X with a mass of 68 and he also predicted that an oxide would have a formula X203 on the modern table i think the element that Mendeleev predicted is (GA) Gallium

Closing a ring restricts the rotation around individual car bon carbon bonds hope it will you !