Question

The approximate atomic weight of electron or positron per mole is:
\[
  A.{\text{ }}5.48 \times {10^{ - 6}}gmo{l^{ - 1}} \\
  B.{\text{ }}5.48 \times {10^{ - 8}}gmo{l^{ - 1}} \\
  C.{\text{ }}5.48 \times {10^{ - 4}}gmo{l^{ - 1}} \\
  D.{\text{ None of these}} \\
 \]

Answer 1

Hint- In order to find the atomic weight of electron, first we will understand the basic definition of electron then we will proceed further by multiplying the mass of electron by Avogadro's number in order to find the atomic weight of electron or positron per mole.

Complete answer:
Electron : An electron is a negatively charged subatomic particle. It can be either free (not attached to any atom), or bound to the nucleus of an atom. Electrons in atoms exist in spherical shells of various radii, representing energy levels. The charge on a single electron is considered as the unit electrical charge.
As we know that
Mass of one electron $ = 9.1 \times {10^{ - 27}}g$
As we know that one mole of electrons contains Avagadro’s number of electrons.
So, mass of one mole of electron $ = m \times Na$ --- (1)
Where m is the mass of each electron and Na is the Avagadro’s number which is equal to $6.023 \times {10^{23}}$
So let us now substitute the values in equation (1) to find the atomic weight of electrons per mole.
Mass of one mole of electron:
$
   = m \times Na \\
   = 9.1 \times {10^{ - 27}}g \times 6.023 \times {10^{23}} \\
   = 5.48093 \times {10^{ - 4}}g/mol \\
   \simeq 5.48 \times {10^{ - 4}}gmo{l^{ - 1}} \\
 $
Hence, the approximate atomic weight of electron or positron per mole is $5.48 \times {10^{ - 4}}gmo{l^{ - 1}}$
So, the correct answer is option C.

Note- The mole is the unit of measurement for the amount of substance in the International System of Units. A mole of a substance or a mole of particles is defined as exactly $6.023 \times {10^{23}}$ particles, which may be atoms, molecules, ions, or electrons. This number is called Avagadro’s number. Students must remember the value of Avagadro’s number to solve such problems related to mole concept.