After 10 years, the isotope would have had two half lives. For each half life, half of the material reacts. Therefore, after one half life, 50% remains. Then, after a second, 25% remains. D is the correct answer.
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Yes, Only bacteria can convert molecular nitrogen, into a form which can be utilized by other living beings such as plants. The nitrogen fixed by the bacteria, by this process, become available to the plants, which uptakes it, for their own growth, and is also accumulated in their seeds. Further, leguminous plants have nitrogen-fixing bacteria associated with them in synergy. They provide the plant with additional nitrogen, and in exchange obtain nutrients from the plant, for their growth and division.
        
             
        
        
        
Blood, flowers, bacteria, and skin
        
             
        
        
        
D, because the air s moving as in longitudinal waves which means <span>a wave vibrating in the direction of propagation, and probation means that the making of more and replacing</span>