Atomic mass Calcium = 40.078 a.m.u
40.078 g ---------------- 6.02x10²³ atoms
165 g -------------------- ??
165 x ( 6.02x10²³) / 40.078 => 2.47x10²⁴ atoms
hope this helps!
        
             
        
        
        
83.9 is the answer i’m pretty sure
        
             
        
        
        
The correct answer would be the last option. A double displacement type of reaction involves the switching of places the cations and anions accordingly. The given reaction is erroneous since in the product side the anions and cations are being paired which would not make sense. The correct reaction should be 
4NaBr + Co(SO3)2 yields <span>CoBr4 + 2Na2SO3</span>
        
             
        
        
        
Answer:
7 is the mass number of li and 3 is the atomic number 
a 3
b 7
c 3
d 4