Which of the following is a synthesis reaction? c2h4 + 3o2 yields 2co2 + 2h2o 2hbr yields h2 + br2 co2 + h2o yields h2co3 f2 + 2 hcl yields cl2 + 2hf

CO2 + H2O yields H2CO3 is a synthesis reaction.

Aphysical change is one that you can put in and remove like a ham sandwich. the stuff you put in there can be changem its not permanet. a chemical change is on that can't be change thats permanet. like when you make a cake and bake it. you can't get those ingredients back.