Question

The particle which has no charge and negligible rest mass are:
(A) $\sigma - meson$
(B) K-meson
(C) Positron
(D) Neutrino

Answer 1

Hint
Particle has 0 charge and mass is almost negligible. We have to tell the name of that particle. We will analyse that the name of that particle is neutrino.

Complete step by step answer
$\sigma - meson$ can have a charge equal to positive, negative, and sometimes neutral also. K-meson also are similar to them and can have a positive, negative, and neutral charge. Positron is antimatter and it is formed in the case of $\beta$ decay. It is released with an electron and thus has the same mass and charge as that of an electron. The only difference between this and an electron is that positron is positively charged and electrons are negatively charged. Neutrinos are very similar to an electron but they do not have any charge on them. Also, they have very little rest mass which can even be zero sometimes. They are really abundant in the universe but they do not react with matter easily. Due to this property, they are incredibly hard to detect. Therefore, the option with the correct answer is option D.
Neutrinos are very tiny. They can penetrate through almost all the baryons. Their mass is in the order of Kilo electron Volts. They are also sometimes attributed as the lightest particles known.

Note:
From the options given we know that $\sigma - meson$ and K-meson are charged particles. So, (A) and (B) cannot be a correct option. Positrons are of mass equal to electrons which we know is more than that of neutrinos. Both mesons have comparable masses, hence (C) cannot be a correct option. The only left ones are neutrinos which stand out as the only correct candidate I.e. option (D).