Single and Double Replacement reactions are exactly as they sound - they “replace” one or two components, depending on the type, with something else obtained in the reaction.
1. This is a double replacement reaction - see that the SO4 and the OH groups are trading what they’re paired with? OH starts paired with Aluminum, and ends up paired to the Hydrogen, and the SO4 starts with the Hydrogen, but ends up with the Aluminum. Two things being replaced - a double replacement reaction.
2. This is a single replacement reaction - Iron replaces the Hydrogen through the reaction, leaving the Hydrogen inbound afterwards; one thing being replaced - a single replacement reaction.
3. Like 1, this is a double replacement reaction - Fluorine and Oxygen trade partners. Two things being replaced - a double replacement reaction.
Number 4 isn’t complete, and I’m not sure about the goal of the practice problems, so I hope this helps enough to finish the work!
