is congress the appropriate institution to have power over immigration and naturalization? why or why not?

Yes, they are.

Explanation:

Congress is a part of the legislative branch. Which means that they're the one that's responsible in creating laws/regulations.

Policies regarding immigration and naturalization be really depended on the current situation. Having the ability to impose that policies into law in an efficient manner is why congress is the appropriate institution to control them.

For example, during the corona virus pandemic, we need to quickly prevent immigrations from high infection rate into the country. Congress could make a legislation that limit the amount of immigrants that could come into the country.

representative government

i believe it is capitalists.