At a fixed temperature and pressure, a cylinder contains equal volumes of O2 and an unknown gas. The identity of the unknown gas CO.
The number of moles of a given substance is calculated by dividing the mass by the molar mass.
The number of moles of O₂ = 
= 0.625 moles.
Based on the given assumption, at fixed temperature and pressure;
- Let assume that the number of moles of the unknown gas is = 0.625 moles
The molar mass of the unknown gas can be estimated as:


= 28 g/mol
Therefore, we can conclude that the unknown gas is CO.
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The formula of density is mass / volume
This means that
- high mass, low volume = high density
- high mass, high volume = so-so
- low mass, high volume = low density
From the graph shown,
D has the lowest density because it has low mass yet high volume.
Answer:
Valence electrons. they can be used to determine the group of an element.
Explanation: