Question

Assertion: 20 gm of Argon (atomic mass of Ar = 40) occupies a volume of $22400c{{m}^{3}}$at STP.
Reason: 20 gm of Neon (atomic mass of Ne = 20) occupies a volume of $22400c{{m}^{3}}$ at STP.
(A)- Both Assertion and Reason are correct and Reason is the correct explanation for Assertion.
(B)- Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion.
(C)- Assertion is correct but Reason is incorrect.
(D)- Assertion is incorrect but Reason is correct.
(E)- Both Assertion and Reason are incorrect.

Answer 1

We will compare the given molecules (Argon and Neon) using the mole concept. The mole concept is a convenient way of expressing the amount of a particular substance.

Complete step by step answer:
-The mole is essentially the count of particles present in a given amount of sample. For example, a solution may have a certain number of dissolved molecules that are more or less independent of each other, similarly a solid has constituent particles that are fixed and bound in a lattice. To give the amount for the substance, the concept of a mole was introduced.
-One mole of a substance can be defined on three different basis-
(i) In terms of particles, one mole of any substance will have a number of particles equal to the Avagadro’s constant. The proportionality factor that relates the number of constituent particles (usually molecules, atoms, or ions) in a sample with the amount of substance in that sample is known as the Avogadro constant. Avogadro number which is denoted as ${{N}_{0}}\text{ or }{{N}_{A}}$is thus the number of particles that are contained in one mole and is exactly equal to $6.02214076\times {{10}^{23}}(6.022\times {{10}^{-23}})$.
(ii) In terms of volume, one mole of any gas will occupy 22.4 L $(22400c{{m}^{3}})$ of gas at (Normal Temperature and Pressure) N.T.P or Molar volume. The volume divided by the amount of substance at a given temperature and pressure is known as the molar volume and is denoted by ${{V}_{m}}\text{ or }\widetilde{V}$.
(iii) In terms of mass, one mole of any substance is equal to the 1 gram of atoms, or 1 gram mole of an atom or 1 gram formula mass of the substance.
-Comparing Argon and Neon in terms of mole-
The number of moles in 20 gm of Argon $=\dfrac{\text{Given mass }}{\text{Molar mass}}=\dfrac{20}{40}=0.2moles=11200c{{m}^{3}}$ at STP.
The number of moles in 20 gm of Neon $=\dfrac{\text{Given mass }}{\text{Molar mass}}=\dfrac{20}{20}=1mole=22400c{{m}^{3}}$at STP.

Therefore, the statement given in Assertion is incorrect and Reason is the correct statement.

So, the correct answer is “Option C”.

Note: Mole concept since is adopted by the International System of Units, but it has numerous criticisms which are as follows-
(i) The number of molecules in a given amount of material is fixed, but the mole is a dimensionless quantity that can only be expressed as a number, not with a distinct base unit.
(ii) The official mole is based on an outdated continuum and is not a fully atomistic concept of matter.
(iii) The SI thermodynamic mole is irrelevant with respect to analytical chemistry and can cause avoidable costs to the economy.
(iv) The mole is not a true metric unit, it is rather a parametric unit.