Answer:
The pair co,Ni is out of order in terms of atomic mass
Explanation:
For co,Ni
Atomic mass of Co = 58.9331 u
Atomic mass of Ni = 58.6934
For Li,be
Atomic mass of Li = 6.941 u
Atomic mass of  be = 9.012182 u
For I,xe
Atomic mass of I =  126.90447 u
Atomic mass of Xe = 131.293 u
Hence, the pair co,Ni is out of order in terms of atomic mass
 
 
        
             
        
        
        
The answer is letter A definitively .
        
             
        
        
        
The average atomic mass of the imaginary element : 47.255 amu
<h3>Further explanation  </h3>
The elements in nature have several types of isotopes  
Isotopes are elements that have the same Atomic Number (Proton)  
Atomic mass is the average atomic mass of all its isotopes  
Mass atom X = mass isotope 1 . % + mass isotope 2.% ..
isotope E-47 47.011 amu, 87.34%
isotope E-48 48.008 amu, 6.895
isotope E-49 50.009 amu, 5.77%
The average atomic mass :

 
        
             
        
        
        
True, because if it wasn't a chemical reaction it would have proceeded to stay the same. but it begins to bubble. 
sorry if this isn't the best answer I'm trying my best.
        
                    
             
        
        
        
Answer:
So, 10 mole of water will weigh (18x10) = 180g.