In the first party system, federalists versus republicans, which party was the “liberal” party in terms of wanting to use the power of the federal government and which was the “conservative” party?

Well at that time the Republicans were the liberals one Republicans wanted the government too help in it's endeavors now since this is before the Civil War one things the Republicans wanted to do was end slavery and give slave human rights. Federalist (later known as the democrats) were conservative and were especially huge in the south the Federalist wanted to keep slavery and limit power of the government.

To summarize

Republicans = Liberals

Federalist(Democrats) = Conservative

the answer to this question is the third option. hope this