The Rocks have remained on top of the screen, while the sand and water have passed through it.
 
        
                    
             
        
        
        
<span>Because
the question is asking moles of NH3, the compound, any subscripts are
irrelevant. It only wants to know how many moles of NH3 molecules, not
individual atoms. 
Therefore, we can simply convert to moles. 1.5x10^23/6.022x10^23 = .249 moles of NH3. 
(If it were to ask moles of Hydrogen, for example, you would multiply
the answer by 3, because there are 3 atoms of Hydrogen per one molecule
of NH3. But this only asks for moles of the entire compound).   
hope you have a great day! :)
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Hope my answer helped you
        
             
        
        
        
Kiloliters and megaliters
        
             
        
        
        
<u>We are given:</u>
Mass of ice = 21 grams
The ice is already at 0°c, the temperature at which it melts to form water
Molar heat of fusion of Ice = 6.02 kJ/mol
<u>Finding the energy required:</u>
<u>Number of moles of Ice: </u>
Molar mass of water = 18 g/mol
Number of moles = given mass/ molar mass
Number of moles = 21 / 18 = 7/6 moles
<u>Energy required to melt the given amount of ice:</u>
Energy = number of moles * molar heat of fusion
Energy = (7/6) * (6.02)
Energy = 7.02 kJ OR 7020 joules