Explanation:
Gas bubbles can appear, there may be a color change, there may be a temperature change, there could be the production of light, volume change, change in smell or taste, or formation of a precipitate. 
In a chemical change, atoms react with each other to form a new substance/product.
 
        
             
        
        
        
Recorded by a seismograph.
        
             
        
        
        
Answer: 63.26%
Explanation:
If we let the abundance of the first isotope be x, then:

Which is equal to <u>63.26%</u>