Answer :
Step 1
It is known that at STP:
1 mole of any gas = 22.4 L
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Step 2
Information provided:
4.16 L of O2
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Information needed:
The molar mass of H2O = 18.0 g (please, the periodic table is useful here)
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Step 3
By stoichiometry,
C3H8 + 5 O2 => 3 CO2 + 4 H2O (the reaction is completed and balanced)
5 x 22.4 L O2 ------------ 4 x 18.0 g H2O
4.16 L O2 ------------ X
X = 4.16 L O2 x 4 x 18.0 g H2O/5 x 22.4 L O2
X = 2.67 g H2O
Answer: 2.67 g H2O