[rsynnott]

> Is this tax sized to cover for that externalities

No, nothing like it. The final costs to the state of excessive sugar consumption are _vast_. This levy is primarily to discourage people from consuming loads of sugar.

> Is the collected money exclusively used to counter the externalities

While I don't know, I'd be very surprised. That sort of bucketed approach to tax collection/use is _extremely_ inefficient; the only place it can possibly be justified is social insurance.