Chatter Answers - Is it available for Salesforce Platform edition
From the documentation:
Chatter Answers is available in: Enterprise, Developer, Performance, and Unlimited Editions.
So no, it is not available. Among other reasons, it requires Cases.
According to Salesforce Communities - License Features, Communities aren't available at all for Group or Professional Editions. In How to Select the Right Sales Cloud Edition, According to page 2, Chatter Answers is available for Customer Communities, Customer Plus Communities, and Partner Communities; all of which are require an additional license. Finally, that document also indicates those Communities are only available for Enterprise and Unlimited Editions.
To be safe, check with your SF customer service rep to verify this as things seem to change frequently.