which must be the same when comparing 1 mol of oxygen gas, o₂, with 1 mol of carbon monoxide gas, co?\no the…

Explanation:

Step1: Recall Avogadro's number

1 mole of any substance contains Avogadro's number ($N_A = 6.022\times 10^{23}$) of entities (atoms, molecules etc.).

Step2: Analyze mass

The molar - mass of $O_2$ is $M_{O_2}=2\times16\ g/mol = 32\ g/mol$, and the molar - mass of $CO$ is $M_{CO}=12 + 16\ g/mol=28\ g/mol$. So, 1 mol of $O_2$ and 1 mol of $CO$ have different masses.

Step3: Analyze volume

The volume of a gas depends on temperature and pressure (using the ideal gas law $PV = nRT$). Without the same temperature and pressure conditions, we cannot say the volumes are the same.

Step4: Analyze number of molecules

Since 1 mol of $O_2$ and 1 mol of $CO$ both contain Avogadro's number of molecules ($6.022\times 10^{23}$ molecules), the number of molecules is the same.

Step5: Analyze number of oxygen atoms

1 mol of $O_2$ contains $2\times6.022\times 10^{23}$ oxygen atoms, and 1 mol of $CO$ contains $6.022\times 10^{23}$ oxygen atoms. So, the number of oxygen atoms is different.

Answer:

the number of molecules