Which of the following sub-atomic particles is not considered a fundamental constituent of a standard atom?

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.

The size of the nucleus is measured in

Calculate the mass of $1$ mole of neutrons in $kg$. $\left( m_n = 1.675 \times 10^{-27} \ kg \right)$

Which of the following particles is represented by the symbol $\alpha$?

The radius of an atom is of the order of