An atom is defined as :

Which of the following statements is correct about the cathode rays?
$1$. These rays start from anode and move towards cathode.
$2$. They are visible with human eye.
$3$. In presence of electric and magnetic fields,they behave like positively charged particles.
$4$. Their characteristic does not depend on the nature of material at electrode.

An electron has mass $m$ and charge $e$. If it is accelerated from rest through a potential difference of $V$,what velocity will it attain?

The mass of an atom is constituted mainly by

Which of the following statements regarding cathode rays is incorrect?

Which of the following particles cannot be accelerated by an electric or magnetic field?