\(1.80 \,g\) દ્રાવ્ય \(A\)ને \(62.5\,cm^3\) ઈથેનોલમાં આગાળવામાં આવે છે અને આ દ્રાવણનું ઠારણ બિંદુ \(155.1 \,K\) માલુમ પડ્યું. તો દ્રાવ્ય \(A\)નું મોલર દળ \(....\,g mol ^{-1}\)માં શોધો. (આપેલઃ ઈથેનોલનું ઠારણ બિંદુ \(156.0\, K\), ઈથેનોલની ધનતા \(0.80\, g\, cm ^{-3}\), ઈથેનોલનો ઠારબિંદુ અવનયન અચળાંક \(2.00\, K\, kg \,mol ^{-1}\) )

A \(81\)
B \(80\)
C \(82\)
D \(83\)

Verified Solution

Answer & Solution

Correct Answer

(B) \(80\)

Step-by-step Solution

Detailed explanation

Mass of \(C _{2} H _{5} OH =62.5 \times 0.8=50\,g\) \(\Delta T _{ f }= K _{ f } \times m\) \(0.9=2 \times \frac{1.8 \times 1000}{ M _{ \pi } \times 50}\) \(M _{ w }=\frac{2 \times 1.8 \times 1000}{0.9 \times 50}=80\)

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

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