Gas falls into scope 1 as the emissions are created on site. For example, when using a gas boiler to provide heating and hot water, the natural gas is combusted at source and therefore a direct emission in your control.
Electricity is classified as an indirect emission, and therefore scope 2 as the electricity is generated elsewhere.
If you want to read more about the different scopes, please visit scopes section of the National Grid Webstie [here].