Given below are two statements: One is labelled as Assertion A and the other is labelled as Reason R. Assertion A: Amongst $\mathrm{He}, \mathrm{Ne}, \mathrm{Ar}$ and Kr ; 1 g of activated charcoal adsorbs more of Kr . Reason R : The critical volume $\mathrm{V}_{\mathrm{c}}\left(\mathrm{cm}^{3} \mathrm{~mol}^{-1}\right)$ and critical pressure $\mathrm{P}_{\mathrm{c}}(\mathrm{atm})$ is highest for Krypton but the compressibility factor at critical point $\mathrm{Z}_{\mathrm{c}}$ is lowest for Krypton. In the light of the above statements, choose the correct answer from the options given below.

(A) $\mathbf{A}$ is true but $\mathbf{R}$ is false

(B) $\mathbf{A}$ is false but $\mathbf{R}$ is true

(C) Both $\mathbf{A}$ and $\mathbf{R}$ are true but $\mathbf{R}$ is NOT the correct explanation of $\mathbf{A}$

(D) Both $\mathbf{A}$ and $\mathbf{R}$ are true and $\mathbf{R}$ is the correct explanation of $\mathbf{A}$

JEE Main · 2023 · 01 Feb 2023 · Shift 1 · States of Matter

Given below are two statements: One is labelled as Assertion A and the other is labelled as Reason R.

Assertion A: Amongst

He, Ne, Ar

and Kr ;
1 g of activated charcoal adsorbs more of Kr .
Reason R : The critical volume

V_{c} (cm^{3} mol^{- 1})

and critical pressure

P_{c} (atm)

is highest for Krypton but the compressibility factor at critical point

Z_{c}

is lowest for Krypton.
In the light of the above statements, choose the correct answer from the options given below.

(A) $A$ is true but $R$ is false✓ Correct
(B) $A$ is false but $R$ is true
(C)Both $A$ and $R$ are true but $R$ is NOT the correct explanation of $A$
(D)Both $A$ and $R$ are true and $R$ is the correct explanation of $A$

Answer: (A)

Solution

Among the noble gases He, Ne, Ar and Kr, krypton is the largest and most polarizable atom, so it experiences the strongest van der Waals forces and is the most easily liquefied; the extent of physical adsorption on activated charcoal runs parallel to this, so one gram of charcoal takes up krypton to the greatest extent and the assertion holds. The critical volume and critical pressure do increase with atomic size and are largest for krypton, but the critical compressibility factor

Z_{c} = \frac{p _{c} V _{c}}{R T _{c}}

is very nearly the same for every gas, lying close to

0.29

for all the noble gases, so singling out krypton as having the lowest value is not a valid distinction and the reason fails. Thus the assertion is true while the reason is false.

JEE Main · 2023 · 01 Feb 2023 · Shift 1 · Single correct option

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JEE Main · 2023 · 01 Feb 2023 · Shift 1 · States of Matter

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