Democritus (460-370 BC) was a Greek philosopher who theorized that all matter could be reduced to particles that could not be divided, which he described as “atomos.” 
John Dalton (1766-1844) Proposed the atomic theory.
        
             
        
        
        
Answer:
nickel is the correct answer
 
        
             
        
        
        
Answer is: <span>concentration of fluoride in the water in parts-per-million is 1 ppm.
</span>Parts-per-million (10⁻⁶) is<span> present at one-millionth of a </span>gram per gram of sample solution, f<span>or example mg/kg.
</span>m(fluoride) = 500 g · 1000 mg/g = 500000 mg.
m(water) = d(water) · V(water).
m(water) = 1 kg/L · 500000 L.
m(water) = 500000 kg.
arts-per-million = 500000 mg ÷ 500000 kg = 1 mg/kg = 1 ppm.
        
             
        
        
        
Answer:
I don't know chemistry
Explanation:
because this is the hardest subject in the world nobody can solve it so do yourself ok Beta 
 
        
                    
             
        
        
        
Lewis Structure is drawn in following steps,
1) Calculate Number of Valence Electrons:    # of Valence electrons in Mg  =  2
# of Valence electrons in I      =  7
# of Valence electrons in I      =  7
                                               ---------
Total Valence electrons          =  16
2) Draw Mg as a central atom surround it by two atoms of Iodine.3) Connect each Iodine atom to Mg, and subtract two electrons per bond. In this case we will subtract 4 electrons from total valence electrons. i.e.
Total Valence electrons           16
- Four electrons                    -   4
                                              ----------
                                                  12
4) Now start adding the remaining 12 electrons on more electronegative atoms i.e. Iodine. 
The final lewis structure formed is as follow,