Mercantilism promoted the idea that national wealth was based ona.a favorable balance of exports over imports b.imperial taxation c.foreign...

The correct answer here has to got to be A -- a favorable
balance of exports over imports.  In other words, you get rich by exporting more to
other countries than you import from them.

This was the
major economic idea back in most of the 18th century.  And it is one reason why
countries took colonies.  They wanted to have colonies where they could buy things
cheaply (things like raw materials) and where they would be the only ones who could sell
manufactured goods.  This would give them a favorable balance of trade and make them
rich.