Here's what's missing and how to approach the problem:

1. Units for Hydrogen:

* 300 H2 is incomplete. You need to specify the units of hydrogen, for example:

* 300 grams of H2

* 300 moles of H2

2. Balanced Chemical Equation:

* You need the balanced chemical equation for the reaction between iron oxide (Fe3O4) and hydrogen (H2). The reaction produces iron (Fe) and water (H2O).

Here's how to solve the problem once you have the complete information:

1. Write the balanced chemical equation:

Fe3O4 + 4H2 → 3Fe + 4H2O

2. Convert the given amount of H2 to moles:

* If you're given grams of H2, use the molar mass of H2 (2.016 g/mol) to convert to moles.

* If you're given moles of H2, you're already in the right units.

3. Use the mole ratio from the balanced equation:

* The equation shows that 4 moles of H2 react with 1 mole of Fe3O4.

4. Calculate the moles of Fe3O4 required:

* Divide the moles of H2 by 4 to find the moles of Fe3O4.

5. Convert moles of Fe3O4 to grams:

* Multiply the moles of Fe3O4 by the molar mass of Fe3O4 (231.53 g/mol) to get the mass in grams.

Example:

Let's say you have 300 grams of H2:

1. Moles of H2: 300 g H2 / 2.016 g/mol = 148.8 mol H2

2. Moles of Fe3O4: 148.8 mol H2 / 4 = 37.2 mol Fe3O4

3. Grams of Fe3O4: 37.2 mol Fe3O4 * 231.53 g/mol = 8604.3 g Fe3O4

Therefore, you would need approximately 8604.3 grams of Fe3O4 to react completely with 300 grams of H2.