Question

Which among the following is the lightest particle :

• A. Neutron
• B. Proton
• C. Electron
• D. Meson

Hint:

Comparing the masses of common subatomic particles:
{Electron:} Very, very light (approx. \(9.1 \times 10^{-31}\) kg).
{Proton:} Much heavier than an electron (approx. 1836 times heavier, \(\sim 1.672 \times 10^{-27}\) kg).
{Neutron:} Slightly heavier than a proton (\(\sim 1.674 \times 10^{-27}\) kg).
{Mesons:} A family of particles with masses typically between that of an electron and a proton/neutron. Even the lightest ones (pions) are over 200 times heavier than an electron. The electron is the lightest of these.

Answer 1

The Correct Option is C

Concept: This question compares the masses of subatomic particles. Protons, neutrons, and electrons are the fundamental constituents of atoms. Mesons are a type of subatomic particle composed of a quark and an antiquark. Step 1: Approximate masses of common subatomic particles
Electron (\(e^-\)): Mass \(\approx 9.109 \times 10^{-31} \text{ kg}\). This is often considered as approximately \(1/1837\) of the mass of a proton.
Proton (\(p^+\)): Mass \(\approx 1.6726 \times 10^{-27} \text{ kg}\). This is approximately 1 atomic mass unit (amu).
Neutron (\(n^0\)): Mass \(\approx 1.6749 \times 10^{-27} \text{ kg}\). The neutron is slightly more massive than the proton, but their masses are very similar (also approx. 1 amu).
Meson: Mesons are a broad category of subatomic particles. Their masses vary depending on the type of meson, but they are generally intermediate between the mass of an electron and the mass of a proton/neutron. For example:
Pion (\(\pi\)-meson): Mass \(\approx 2.4 \times 10^{-28} \text{ kg}\) (approx. 264 times the electron mass, or 1/7 of proton mass).
Kaon (K-meson): Heavier than pions. Even the lightest mesons (pions) are significantly more massive than electrons. Step 2: Comparing the masses
Mass of Electron: \(\sim 9.1 \times 10^{-31} \text{ kg}\)
Mass of Proton: \(\sim 1.67 \times 10^{-27} \text{ kg}\)
Mass of Neutron: \(\sim 1.67 \times 10^{-27} \text{ kg}\)
Mass of typical Meson (e.g., pion): \(\sim 2.4 \times 10^{-28} \text{ kg}\) Comparing the powers of 10, \(10^{-31}\) is much smaller than \(10^{-28}\) or \(10^{-27}\). The order of masses is approximately: Electron<Meson (pion)<Proton \(\approx\) Neutron. The handwritten note "e<p<n" on the image (implying mass comparison, though typically p \(\approx\) n with n slightly heavier) supports that electron is the lightest of these three. Step 3: Identifying the lightest particle The electron has by far the smallest mass among the options listed (and among the fundamental constituents of an atom).