Answer
720.9 mmHg
Explanation
Gas collected over water must always account for the saturated vapor pressure.
Note that the saturated vapor pressure of water at 23 °C = 21.1 mm Hg.
Therefore atmospheric pressure is
[tex]Atmospheric\text{ }pressure=P_{SVP}-P_{nitrogen}[/tex]
The atmospheric pressure given = 742 mmHg, Psvp = 21.1 mmHg, thus, we
[tex]\begin{gathered} 742mmHg=21.1mmH-P_{nitrogen} \\ \\ P_{nitrogen}=742mmHg-21.1mmHg \\ \\ P_{nitrogen}=720.9\text{ }mmHg \end{gathered}[/tex]
