Final answer:
In British slang, 'Ta' means thank you and 'Ta Ta' is used to say good-bye.
Step-by-step explanation:
In British slang, the word 'Ta' alone means thank you; when you say it twice (Ta Ta), it means good-bye. The other options given, such as 'Oi', 'No', and 'Eh' do not have these meanings. 'Oi' is often used to get someone's attention, 'No' is a straightforward negative response, and 'Eh' can be used to ask for repetition or clarification or to express lack of understanding or surprise.