How can you tella gas is given off in an experiment?

Answer 1

There are a number of ways to observe the release of a gas. If you perform your experiment underwater, you can see the bubbles that a gas will form. In a sealed container, the release of a gas will increase the pressure in the container (and can do so sufficiently to cause an explosion, in some cases). Some gases (such as nitric oxide) are visible. Many gases have a detectable odor. Chlorine gas can be observed either visually (it is green) or by smell (it causes a choking sensation). Cyanogen can be observed by the people who drop dead when they inhale it. So there are many different methods.