The gas evolved when dilute HCl reacts with active metal is

The Hydrogen gas evolved when dilute HCl reacts with active metal.

Active metals are generally good reducing agents because they readily lose electrons. When an active metal combines with hydrochloric acid, the metal becomes ionized and gives electrons to the acid's hydrogen ions. Upon reaction of dilute hydrochloric acid with active metal, chloride salt of that acid is formed with the release of hydrogen gas. 

Example: $2\mathit{Zn}+2\mathit{HCl}\to 2\mathit{ZnCl}+H_2$
In this case, zinc is an active metal that combines with hydrochloric acid to generate the equivalent zinc salt, zinc chloride, as well as hydrogen gas.