Welcome to your CHEMISTRY Your Name What is the chemical formula of water? a) H₂O b) CO₂ None Which gas is essential for respiration? Oxygen (O₂) Nitrogen (N₂) None Which acid is found in lemon? Citric acid Sulfuric acid None What is the atomic number of carbon? 6 8 None Which element is a noble gas? Helium (He) Sodium (Na) None None Please fill in the comment box below. Time's upTime is Up!