Is Scarlett 2i2 compatible with Audacity?
In short, you can use your Focusrite interface with Audacity, but you will only be able to use the first two inputs and outputs. As OS X's inbuilt audio driver (Core Audio) is able to support multichannel input/output, Audacity will see all inputs and outputs of any Scarlett / Saffire / Clarett interface.
How do I get Audacity to recognize focusrite?
1) First ensure you have downloaded and installed the driver for your interface (https://focusrite.com/downloads), then connect your interface. 2) Open Audacity and check that 'MME' is selected and the 'Focusrite USB' option has been set as the Input and Output device.