Who discovered oxygen in 1774?

• A. Antoine Lavoisier
• B. Joseph Priestley
• C. Robert Boyle
• D. Carl Scheele

Answer: (B)

The main idea here is identifying who first published the discovery of a life-supporting gas in 1774. Joseph Priestley conducted experiments that released a gas when heating mercuric oxide and, in 1774, published his findings naming the gas dephlogisticated air. This work provided the first widely recognized demonstration that a distinct component of air could support combustion and life, which we now call oxygen. Although Carl Wilhelm Scheele had produced the gas earlier, his results were published later—in 1777—so Priestley is credited with the 1774 discovery. Antoine Lavoisier later clarified its role and gave it the name oxygen, but he did not make the initial discovery or publish it in 1774.