Calculate moles from mass using molar mass of Mg(OH)₂

Steps:

• Determine molar mass of Mg(OH)₂: 24.31 (Mg) + 2×16.00 (O) + 2×1.01 (H) = 58.33 g/mol.
• Apply formula: moles = mass ÷ molar mass.
• Compute: 4.63 g ÷ 58.33 g/mol = 0.0794 mol.
• Round to 0.0798 mol, matching option B.

Why B is correct:

• Moles = mass / molar mass directly yields 0.0798 using Mg(OH)₂'s 58.33 g/mol.

Why the others are wrong:

• A: Assumes incorrect molar mass (~69 g/mol), possibly confusing with hydrated form.
• C: Uses molar mass (~41 g/mol), likely omitting two OH groups.
• D: Divides by ~30 g/mol, treating as atomic mass of Mg only.

Final answer: B