An unknown element was collected during a chemical reaction. The sample of the unknown element with a mass of 4.00 g was then allowed to react with excess oxygen, forming an oxide with a mass of 6.63 g. The oxide contains an equal amount (in mol) of both elements (the unknown element and oxygen). Identify the unknown element.

To identify the unknown element, we need to follow these steps:

1. First, we need to find the mass of oxygen that reacted with the unknown element. We do this by subtracting the mass of the unknown element from the mass of the oxide. So, 6.63 g (mass of the oxide) - 4.00 g (mass of the unknown element) = 2.63 g of oxygen.

2. Next, we need to convert the mass of oxygen to moles. We know that the molar mass of oxygen is 16.00 g/mol, so we divide the mass of oxygen by its molar mass. So, 2.63 g ÷ 16.00 g/mol = 0.164 mol of oxygen.

3. The problem states that the oxide contains an equal amount (in mol) of both elements. This means that there are also 0.164 mol of the unknown element.

4. Now, we can find the molar mass of the unknown element by dividing its mass by the number of moles. So, 4.00 g ÷ 0.164 mol = 24.39 g/mol.

5. Finally, we compare this molar mass with the molar masses of known elements. The molar mass of 24.39 g/mol is closest to the molar mass of magnesium (24.31 g/mol), so the unknown element is likely magnesium.