(b). That's right. A Tax File Number (TFN) is a number issued by the Australian Taxation Office (ATO) to identify individuals, companies and others who lodge income tax returns with the ATO. These unique identifying numbers allow the ATO to check that taxes are paid at the required rates.

Because a sole proprietorship is not considered to be legally distinct from its owner, and because it is not a 'company', it is the owner of the business who, as an individual, must apply for a Tax File Number.