The density of He is 1.79 x 10⁻⁴ g/mL
In other words in 1 mL there's 1.79 x 10⁻⁴ g of He. 
To fill a volume of 6.3 L the mass of He required 
    = 1.79 x 10⁻⁴ g/mL * 6300 mL
   = 11 277 * 10⁻⁴ g
  Therefore mass of He required = 1.1277 g of He
        
                    
             
        
        
        
69.9%
Explanation:
To find the mass percentage of iron in the compound in Fe₂O₃, we would go ahead to express the given molar mass of the iron to that of the compound. 
  Mass percentage  = 
  x 100
Molar mass of Fe = 55.85g/mol
Molar mass of O = 16g/mol
Molar mass of Fe₂O₃ = 2(55.85) + 3(16) = 159.7g/mol
 Mass percentage  = 
   = 69.94% = 69.9%
learn more: 
Mass percentage brainly.com/question/8170905
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Answer: -
1 mol
Explanation: -
Number of moles of Sulphur S = 7
Number of moles of O2 = 9
The balanced chemical equation for the reaction is
2S (s)+3 O2 (g)→2SO3(g)
From the above reaction we can see that
3 mol of O2 react with 2 mol of S
9 mol of O2 will react with

= 6 mol of S
Unreacted S = 7 - = 1 mol.
If a reaction vessel initially contains 7 mol S and 9 mol O2
1 mole of s will be in the reaction vessel once the reactants have reacted as much as possible
 
        
             
        
        
        
Liquid :) it goes directly from a solid to a gas. Have a nice day!
        
                    
             
        
        
        
Answer: Theoretical Yield = 0.2952 g
                Percentage Yield = 75.3%
Explanation:
Calculation of limiting reactant: 
n-trans-cinnamic acid moles = (142mg/1000) / 148.16 = 9.584*10⁻⁴ mol
pyridium tribromide moles = (412mg/1000) / 319.82= 1.288*10⁻³ mol
- n-trans-cinnamic acid is the limiting reactant
 
The molar ratio according to the equation mentioned is equals to 1:1
The brominated product moles is also = 9.584*10⁻⁴ mol
Theoretical yield = (9.584*10⁻⁴ mol) * (Mr of brominated product)
                              =  (9.584*10⁻⁴ mol) * (307.97) = 0.2952 g
Percentage Yield is : Actual Yield / Theoretical Yield = 0.2223/0.2952
                                                                                            = 75.3%