Moles in 36 g of H₂O (M=18).

**The reasoning** This is a straightforward **mole calculation** using the formula: **Number of moles = Mass / Molar mass** You're given: - Mass of H₂O = 36 g - Molar mass (M) of H₂O = 18 g/mol So: Number of moles = 36 g ÷ 18 g/mol = **2 moles** Think of it like this: if one "pack" of water molecules weighs 18 g, how many packs are in 36 g? Exactly 2 packs! **Why the wrong options tempt you** - **Option A (0.5)**: You might flip the formula and divide 18 by 36 instead. Always put the given mass on top! - **Option B (1)**: Perhaps you forgot to do the division entirely, or confused 18 with 36. - **Option D (4)**: You may have multiplied instead of dividing (36 × something), mixing up the formula direction. **Quick takeaway** **"Moles = Mass over Molar mass"** — write it as n = m/M and you'll never forget which number goes where. If you have more grams than the molar mass, you must have more than 1 mole!