Assertion A: 3.1500\,g of hydrated oxalic acid dissolved in water to make 250.0\,mL solution will result in 0.1\,M…

🧠 Hydrated oxalic acid carries $2\,\ce{H2O}$ Lab oxalic acid is $\ce{H2C2O4 \cdot 2H2O}$. Its molar mass is $90 + 36 = 126\,\text{g/mol}$. Use that to check the assertion.

🗺️ Per-statement check R: Molar mass of hydrated oxalic acid $= 90 + 2 \times 18 = 126\,\text{g/mol}$. True. A: Moles dissolved $= 3.15 / 126 = 0.025\,\text{mol}$. Volume $= 0.25\,\text{L}$. $M = \frac{0.025}{0.25} = 0.1\,\text{M}. \text{ True.}$ Link: A is true because we used $126$ from R. So R explains A.

⚠️ Common mistake Using the molar mass of anhydrous oxalic acid ($90$). Then the moles look like $3.15/90 = 0.035$ and concentration becomes $0.14\,\text{M}$ — wrong. Always include the water of hydration.

$\boxed{\text{Answer: (c)}}$