Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R Assertion A : 3.1500 ~g of hydrated oxalic acid dissolved in water to make 250.0 ~mL solution will result in 0.1 ~M oxalic acid solution. Reason R : Molar mass of hydrated oxalic acid is 126 ~g ~mol^-1 In the light of the above statements, choose the correct answer from the options given below.

Both A and R are true and R is the correct explanation of A

Both A and R are true but R is NOT the correct explanation of A

Some Basic Concepts of Chemistry PYQ — JEE Main 2023 · 10 Apr · Shift 2 · Q5 with Solution

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Correct answer: C

Identify the compound

Hydrated oxalic acid is oxalic acid dihydrate: $\mathrm{H_2C_2O_4\cdot 2H_2O}$
Calculate its molar mass

$M(\mathrm{H_2C_2O_4}) = 2(1) + 2(12) + 4(16) = 2 + 24 + 64 = 90\,\mathrm{g\,mol^{-1}}$

$M(2\mathrm{H_2O}) = 2\times 18 = 36\,\mathrm{g\,mol^{-1}}$

Therefore, $M(\mathrm{H_2C_2O_4\cdot 2H_2O}) = 90 + 36 = 126\,\mathrm{g\,mol^{-1}}$

So, Reason R is true.
Find moles in 3.1500 g hydrated oxalic acid

$n = \frac{3.1500}{126} = 0.0250\,\mathrm{mol}$
Find molarity of the solution

Volume of solution: $250.0\,\mathrm{mL} = 0.2500\,\mathrm{L}$

Molarity: $M = \frac{n}{V} = \frac{0.0250}{0.2500} = 0.100\,\mathrm{M}$

Hence, Assertion A is true.
Check whether R explains A

The assertion is proved directly using the molar mass of hydrated oxalic acid: $\text{Molarity} = \frac{\frac{3.1500}{126}}{0.2500} = 0.1\,\mathrm{M}$

Therefore, the reason correctly explains the assertion.
Final conclusion
- Assertion A: True
- Reason R: True
- R is the correct explanation of A
So the correct option is C.