Answer: Bohr proposed his quantized shell model of the atom to explain how electrons can have stable orbits around the nucleus. 
so C would seems to be right.
Explanation: The energy of an electron depends on the size of the orbit and is lower for smaller orbits. Radiation can occur only when the electron jumps from one orbit to another. The atom will be completely stable in the state with the smallest orbit, since there is no orbit of lower energy into which the electron can jump.
 
        
                    
             
        
        
        
Answer:
The vertical columns of the periodic table are called groups, or families. The significance is elements with similar properties are placed in the same vertical columns. The horizontal rows of the periodic table are called periods. The significance is that properties vary from left to right along the rows.
Explanation:
We just did this in science
 
        
                    
             
        
        
        
Answer:
I believe it's D
Explanation:
they both are worked a lot and it makes the most sense.