You would know a decomposition reaction occurred if the reactants separated. For example from AB → A+B.
Now if you look at your options only 1 works out for that equation. Letter A. 
From the compound K2CO3 it split up to K2O +CO2
It cannot be letter B because synthesis/combination occurred. The same goes for letter C. Letter D, single displacement occurred. 
Again, the answer is A.
        
             
        
        
        
Answer:
the difference of electrical potential between two points.
Explanation:
 
        
             
        
        
        
Answer:
hope it helps...
Explanation:
The Principle of Moments states that when a body is balanced, the total clockwise moment about a point equals the total anticlockwise moment about the same point.
 
        
                    
             
        
        
        
The beginning of the Phanerozoic is marked by the development of hard body parts, such as shells and bones.
        
             
        
        
        
The correct answer is c because B) is a vector which includes both velocity and direction