Table:
text: Timeline of chemical element discoveries
Modern discoveries
Modern discoveries
Z Element_ Observed_or_predicted Isolated_widely_known Observer First_isolator Notes_
1 Hydrogen 1766 1500 H. Cavendish Paracelsus Cavendish was the first to distinguish H , 2 from other gases, although Paracelsus around 1500, Robert Boyle, and Joseph Priestley had observed its production by reacting strong acids with metals. Lavoisier named it in 1793.
8 Oxygen 1771 1771 W. Scheele W. Scheele Obtained it by heating mercuric oxide and nitrates in 1771, but did not publish his findings until 1777. Joseph Priestley also prepared this new air by 1774, but only Lavoisier recognized it as a true element; he named it in 1777.

text: Timeline of chemical element discoveries
Modern discoveries
Modern discoveries
Z Element_ Observed_or_predicted Isolated_widely_known Observer First_isolator Notes_
7 Nitrogen 1772 1772 D. Rutherford D. Rutherford He discovered Nitrogen while he was studying at the University of Edinburgh. He showed that the air in which animals had breathed, even after removal of the exhaled carbon dioxide, was no longer able to burn a candle. Carl Wilhelm Scheele, Henry Cavendish, and Joseph Priestley also studied the element at about the same time, and Lavoisier named it in 1775-6.
17 Chlorine 1774 1774 W. Scheele W. Scheele Obtained it from hydrochloric acid, but thought it was an oxide. Only in 1808 did Humphry Davy recognize it as an element.
25 Manganese 1774 1774 W. Scheele G. Gahn Distinguished pyrolusite as the calx of a new metal. Ignatius Gottfred Kaim also discovered the new metal in 1770, as did Scheele in 1774. It was isolated by reduction of manganese dioxide with carbon.
56 Barium 1772 1808 W. Scheele H. Davy Scheele distinguished a new earth (BaO) in pyrolusite and Davy isolated the metal by electrolysis.

text: Timeline of chemical element discoveries
Modern discoveries
Modern discoveries
Z Element_ Observed_or_predicted Isolated_widely_known Observer First_isolator Notes_
42 Molybdenum 1778 1781 W. Scheele J. Hjelm Scheele recognised the metal as a constituent of molybdena.
52 Tellurium 1782  F.-J.M. von Reichenstein H. Klaproth Muller observed it as an impurity in gold ores from Transylvania.
74 Tungsten 1781 1783 T. Bergman J. and F. Elhuyar Bergman obtained from scheelite an oxide of a new element. The Elhuyars obtained tungstic acid from wolframite and reduced it with charcoal.
38 Strontium 1787 1808 W. Cruikshank H. Davy Cruikshank and Adair Crawford in 1790 concluded that strontianite contained a new earth. It was eventually isolated electrochemically in 1808 by Humphry Davy.

Question: Considering the timeline of chemical element discoveries, which element was observed or predicted by w.scheele in 1771. ?