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Q.
If isobutane and $n$-butane are present in a gas, then how much oxygen should be required for complete combustion of $5$ kg of this gas
Some Basic Concepts of Chemistry
Solution:
Isobutane and $n$-butane $[C_4H_{10}]$ have same molecular formula;
$C_4H_{10} + \frac{13}{2} O_2 \to 4CO_2 + 5H_2O$
For $58\, g$ of $C_4H_{10} \,208 \,g \,O_2$ is required then for $5$ kg of
$C_4H_{10}, O_2$ required $ = \frac{5\times 208}{58} = 17.9\,kg$