Answer: 6.38 moles of
are needed to react with 2.55 mol of 
Explanation:
The balanced chemical reaction for the combustion of ethyne is:

According to stoichiometry:
2 moles of
require = 5 moles of 
Thus 2.55 mol of
require =
moles of 
Thus 6.38 moles of
are needed to react with 2.55 mol of 
b. Pressure
Explanation:
Pressure is a physical effect that can change the boiling point of a substance.
Pressure is the force per unit area on a body.
- A substance will boil when the vapor pressure of its heated molecules is greater than the atmospheric pressure.
- The higher the atmospheric pressure, the higher the temperature and energy required to boil a substance.
- At high altitude, the atmospheric pressure is low and the boiling point of substances is lower.
learn more:
Boiling point brainly.com/question/8567736
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