I’m a little confused on how I should answer the question. Any help?

Which statement about sound is not true? a. air particles travel with sound waves. b. sound waves cannot travel through a vacuum. c. sound waves exist even if no one hears them. d. air particles vibrate along the path of a sound wave.

How many grams of magnesium metal will react completely with 8.3 liters of 5.5 m hcl? show all of the work needed to solve this problem. mg (s) + 2hcl (aq) → mgcl2 (aq) + h2 (g)

What is conserved in the reaction shown below? h2(g) + cl2 (g) --> 2hcl(g)a. mass onlyb. mass and moles onlyc. mass, moles, and molecules onlyd. mass, moles, molecules, and volume