One possibility of why gold price would drop is a large discovery of gold deposits somewhere in the world. Under this circumstance,

what would happen to the money supply? And what about the interest rate?

4.Now, consider this country is running an external deficit (i.e. importing more goods and/or services than exporting them) and the local currency

is depreciating against foreign currency, what would happen to the central bank balance sheet?

5.And what would happen when the external deficit becomes a chronic one?