CREATE TABLE table_202_158 (id NUMBER, "z" NUMBER, "element" CLOB, "observed or predicted" CLOB, "isolated  ( widely known ) " NUMBER, "observer" CLOB, "first isolator" CLOB, "notes" CLOB)

which element was observed or predicted in 1771 by w.scheele ?
SELECT "element" FROM table_202_158 WHERE "observed or predicted" = 1771 AND "observer" = 'w. scheele'
SELECT "element" FROM "table_202_158" WHERE "observed or predicted" = 1771 AND "observer" = 'w. scheele'