How do you do double replacement reactions?

Subduction zones occur on earth where dense oceanic crust dives under more buoyant continental crust. these boundaries are characterized by a deep ocean trench next to a high continental mountain range, large numbers of earthquakes and volcanoes. all of this is further evidence for the a) big bang theory b) origin of the species eliminate c theory of plate tectonics d theory of natural selection 4 sedimentary rocks found high in the himalayen mountain

Areaction in which products can react to re-form reactants is

How many distinct monochlorinated products, including stereoisomers, can result when the alkane below is heated in the presence of cl2? 3 4 5 6 7?