1a One's really commercial, making final billion (6) ?D???B.
3D. Might broker do this with market finally 100 per cent up (5) ??U?T. Looks like ERUPT. (TPURE up) but might brokers erupt?!
First letter is the fourth letter of 1 across.
1 Adverb. It's been answered before - I think the parsing was Advert, commercial,becomes Adverb (making final billion = put a B at the end). 'Really' is an adverb.
I have struggled to satisfy myself with a good parse - yes the 'might' of a volcano 'breaks' the crust of the Earth - but does that make it a 'Broker'?