Answer:
3.91g
Step-by-step explanation:
1. Use the equation mol = mass/Mr (Molecular Formula)
2. Use the information you have and put it into the formula 2.9/23 = 0.1260869565
3. Multiply 0.1260869565 by 62 (molecular formula of Na2O) - Formula rearranged to mass = mol × Molecular formula = 7.817391303
4. Divide by two to get two moles, as shown in the chemical equation
5. 3.9086956515
6. 3.91g to three significant figures