Question:

The minimum amount of \(\mathrm{O_2(g)}\) consumed per gram of reactant is for the reaction :
(Given atomic mass : Fe = 56, O = 16, Mg = 24, P = 31, C = 12, H = 1)

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Compute grams of O2 used per gram of the substance that burns (Fe, P4, C3H8, Mg) for each reaction and pick the smallest.
Updated On: Nov 5, 2026
  • \(\mathrm{4Fe(s)+3O_2(g)\rightarrow 2Fe_2O_3(s)}\)
  • \(\mathrm{P_4(s)+5O_2(g)\rightarrow P_4O_{10}(s)}\)
  • \(\mathrm{C_3H_8(g)+5O_2(g)\rightarrow 3CO_2(g)+4H_2O(l)}\)
  • \(\mathrm{2Mg(s)+O_2(g)\rightarrow 2MgO(s)}\)
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The Correct Option is A

Solution and Explanation

Grams of \(\mathrm{O_2}\) per gram of the fuel:
(A) \(\dfrac{3\times32}{4\times56}=\dfrac{96}{224}=0.43\)
(B) \(\dfrac{5\times32}{124}=\dfrac{160}{124}=1.29\)
(C) \(\dfrac{5\times32}{44}=\dfrac{160}{44}=3.64\)
(D) \(\dfrac{32}{2\times24}=\dfrac{32}{48}=0.67\)
The minimum is for reaction (A).
Answer: (1) \(\mathrm{4Fe(s)+3O_2(g)\rightarrow 2Fe_2O_3(s)}\)
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