Concept:Photosynthesis produces glucose and releases O2 as a by-product.Explanation:In a photosynthesis experiment, a water plant is kept in light and gives off gas bubbles.This gas is collected and tested with a glowing splint.If the splint relights, the gas is oxygen (O2).The release of oxygen (O2) is clear evidence that photosynthesis is taking place.Release of carbon (IV) oxide (CO2) would suggest respiration, not photosynthesis.Answer:B. release of oxygen