Misc: If a dish is served 'au gratin', what does it have on it?

Questions

City, capital of the province of Quebec, Canada, in Quebec county, at the confluence of the Saint Lawrence & Saint-Charles rivers, in the southern part of the province?

Class of complex chemical compounds in plants?

Class of invertebrates belonging to the coelenterate phylum?

Cleopatra used what kind of seeds for lipstick?

Cloud heights are measured by a....?