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3 g of H₂

Explanation:

The balanced equation for the reaction is given below:

Cr₂O₃ + 3H₂ —> 2Cr + 3H₂O

Next, we shall determine the masses of Cr₂O₃ and H₂ that reacted from the balanced equation. This can be obtained as follow:

Molar mass of Cr₂O₃ = (52×2) + (16×3)

= 104 + 48

= 152 g/mol

Mass of Cr₂O₃ from the balanced equation = 1 × 152 = 152 g

Molar mass of H₂ = 2 × 1 = 2 g/mol

Mass of H₂ from the balanced equation = 3 × 2 = 6 g

SUMMARY:

From the balanced equation above,

152 g of Cr₂O₃ reacted with 6 g of H₂

Finally, we shall determine the mass of H₂ needed to covert 76 g of Cr₂O₃. This can be obtained as follow:

From the balanced equation above,

152 g of Cr₂O₃ reacted with 6 g of H₂.

Therefore, 76 g of Cr₂O₃ will react with = (76 × 6) / 152 = 3 g of H₂

Thus, 3 g of H₂ is needed to convert 76 g of Cr₂O₃.