Answer:
![50\text{ molecules}](https://img.qammunity.org/2023/formulas/chemistry/college/b3ahs0h61argctp8n2376afyr21pd3oz42.png)
Step-by-step explanation:
Here, we want to know the number of molecules of oxygen that was reacted with
From the question, we can see that the mole ratio is 2 to 1
Thus, the number of molecules of oxygen reacted will be half that of hydrogen
Hence, the number of molecules of oxygen will be:
![\rightarrow(100)/(2)\text{ = 50 molecules}](https://img.qammunity.org/2023/formulas/chemistry/college/gpneoctwea9dgzs0s12gbbzaxgraiizz0k.png)