Answer:
The transition elements or transition metals occupy the short columns in the center of the periodic table, between Group 2A and Group 3A.Explanation:
 
        
                    
             
        
        
        
The correct answer is D.
Echo refers to the sound that is heard when a sound wave is reflected back from a surface. An echo sound is made when a sound wave traveled through the air, hit a hard surface and get reflected back. Generally, hard surfaces reflect sound wave while soft surfaces absorb sound waves. Reflected sound waves are used in application of some devices that are used in range and direction finding. 
 
 
        
                    
             
        
        
        
There are 66 neutrons in a single atom of indium-115. The atomic number of indium-115 is 49, meaning there are 49 protons. Then the atomic mass is 115, so 115-49 = 66. 
        
             
        
        
        
Hey mate 
This is the answer
The elements potassium and sodium have similar chemical properties because they have the same number of valence electrons and form +1 ions.
Plsssssss mark me as brainliest