Question

Avogadro’s number is NOT equal to:
A. the number of atoms in ${\text{11}}{\text{.2L}}$of ${{\text{O}}_{\text{2}}}$ at STP
B. the number of atoms in ${\text{1 mol}}$of ${\text{He}}$ at STP
C. the number of electrons in ${\text{96,500 coulombs}}$
D. the number of ${\text{S}}{{\text{O}}_{\text{4}}}^{{\text{2 - }}}$ ions in ${\text{1L}}$ of ${\text{0}}{\text{.5M}}$ sulphuric acid

Answer 1

Hint: To come to the solution of the given problem, the concept of Avogadro number should be clear. Avogadro’s number is the number of units in one mole of any substance.

Complete step by step answer: The Avogadro constant is the proportionality factor that relates the number of particles (usually molecules, atoms or ions) in a sample with the amount of substance in that sample.
 Its SI unit is the reciprocal mole (mol).
 It is defined as ${{\text{N}}_{\text{A}}}{\text{ = 6}}{\text{.02214076}} \times {\text{1}}{{\text{0}}^{{\text{23}}}}$.It is named after the Italian scientist Amedeo Avogadro.
Avogadro number = ${{\text{N}}_{\text{A}}}{\text{ = 6}}{\text{.02214076}} \times {\text{1}}{{\text{0}}^{{\text{23}}}}$
One mole of any substance has ${{\text{N}}_{\text{A}}}{\text{ = 6}}{\text{.02214076}} \times {\text{1}}{{\text{0}}^{{\text{23}}}}$ number of atoms, molecules or ions.
Therefore, moles of ${\text{S}}{{\text{O}}_{\text{4}}}^{{\text{2 - }}}$ ions in ${\text{1L}}$ of ${\text{0}}{\text{.5M}}$${{\text{H}}_{\text{2}}}{\text{S}}{{\text{O}}_{\text{4}}}$ are:
${\text{Molarity = }}\dfrac{{{\text{moles}}}}{{{\text{volume}}}}$.
According to the values given in the question, the expression will become:
${\text{0}}{\text{.5 = }}\dfrac{{{\text{moles}}}}{{\text{1}}}$.
That is, the number of moles will be ${\text{0}}{\text{.5 mol}}$.
Hence, according to the Avogadro’s number one mole of every substance is equal to the Avogadro’s constant.
But in given question, ${\text{0}}{\text{.5}}$ moles of ${\text{S}}{{\text{O}}_{\text{4}}}^{{\text{2 - }}}$ ions is not equal to Avogadro’s number.
Whereas in all other options the amount is equal to the Avogadro number of particles.
Therefore, option D matches the condition given in the question.

Note: One mole of any substance is equal to Avogadro’s number. Values should be carefully taken. Moreover, units must be mentioned wherever required. STP or NTP conditions should be taken care of.