Answer:
6.67 moles
Explanation:
Given that:-
Moles of hydrogen gas produced = 10.0 moles
According the reaction shown below:-

3 moles of hydrogen gas are produced when 2 moles of aluminium undergoes reaction. 
Also, 
1 mole of hydrogen gas are produced when  moles of aluminium undergoes reaction.
 moles of aluminium undergoes reaction. 
So, 
10.0 moles of hydrogen gas are produced when  moles of aluminium undergoes reaction.
 moles of aluminium undergoes reaction. 
<u>Moles of Al needed  =  moles = 6.67 moles</u>
 moles = 6.67 moles</u>
 
        
             
        
        
        
Answer:
moles Ar in 20g = 0.500 mole Ar
Explanation:
moles = grams given / formula weight = 20g / 39.948g·mol⁻¹ = 0.500 mole Ar
 
        
             
        
        
        
Answer:
b, H2O(s) r H2O(g)
Explanation:
entropy is heat, so increase in heat would mean water gets evaporated or melted, or both in this case. so the only choice above that showed increase in heat is from solid(ice) to gas(water vaper) due to increase in heat in the reaction. 
 
        
             
        
        
        
The ion N³⁻ is called the azide ion. In its neutral state, it occurs as the element Nitrogen. The atomic number of Nitrogen is 7. When it turns into an anion (negatively charged ion), it gains 3 more electrons. That's why its net charge becomes -3. It means that the protons is still 7, but the electrons are now 10. 
Overall charge = +7 + -10 = -3
        
                    
             
        
        
        
The last set which is n=4 l=3 m=3 is a valid set