Q. Which of the following gases were called Fixed Air by Scottish physician Joseph Black which is discovered in 1750s?
Answer: Carbon Dioxide
Notes: Scottish physician Joseph Black is attributed with the discovery of magnesium, latent heat, specific heat, and carbon dioxide. He found that limestone (calcium carbonate) could be heated or treated with acids to yield a gas he called "fixed air." This fixed air was denser than air and supported neither flame nor animal life. He also found out that when bubbled through limewater, it would precipitate calcium carbonate. He concluded that fixed air is produced by animal respiration and microbial fermentation.