who discover this element?
Carl Axel Arrhenius
Yttrium
In 1787, part-time chemist Carl Axel Arrhenius found a heavy black rock in an old quarry near the Swedish village of Ytterby (now part of the Stockholm Archipelago). 
what is yttrium? Chemical element what are its properties? Soft, silver-metallic, lustrous and highly crystalline transition metal.
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Yttrium [SEP] History
In 1787, part-time chemist Carl Axel Arrhenius found a heavy black rock in an old quarry near the Swedish village of Ytterby (now part of the Stockholm Archipelago). Thinking that it was an unknown mineral containing the newly discovered element tungsten, he named it "ytterbite" and sent samples to various chemists for analysis. Johan Gadolin at the University of Åbo identified a new oxide (or "earth") in Arrhenius' sample in 1789, and published his completed analysis in 1794. Anders Gustaf Ekeberg confirmed the identification in 1797 and named the new oxide "yttria". In the decades after Antoine Lavoisier developed the first modern definition of chemical elements, it was believed that earths could be reduced to their elements, meaning that the discovery of a new earth was equivalent to the discovery of the element within, which in this case would have been "yttrium".