AP EAMCET · Chemistry · p Block Elements (Group 15, 16, 17 & 18)

Assertion (A) Helium has lowest boiling point (4.2 K).
Reason (R) The forces that exist between helium atoms are weak dispersion forces.

A Both (A) and (R) are correct and (R) is the correct explanation of \((A)\).
B Both \((A)\) and \((R)\) are correct but \((R)\) is not the correct explanation of (A).
C \((A)\) is correct but \((R)\) is incorrect.
D (A) is incorrect but \((R)\) is correct

Verified Solution

Answer & Solution

Correct Answer

(A) Both (A) and (R) are correct and (R) is the correct explanation of \((A)\).

Step-by-step Solution

Detailed explanation

Helium has lowest boiling point (4.2 K) because the forces of attraction between \(\mathrm{He}\) atoms are weak dispersion forces. Thus, both assertion and reason are correct and reason \((\mathrm{R})\) is the correct explanation of assertion (A).

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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Assertion (A) Helium has lowest boiling point (4.2 K).Reason (R) The forces that exist between helium atoms are weak dispersion forces.

Step-by-step Solution

Assertion (A) Helium has lowest boiling point (4.2 K).
Reason (R) The forces that exist between helium atoms are weak dispersion forces.