Who discovered the neutron?

Write down the electron distribution of chlorine atom. How many electrons are there in the $L$ shell? (Atomic number of chlorine is $17$).

What do you understand by an octet of electrons in the valence shell?

$A$ helium atom has two electrons in its valence shell,but its valency is not two. Explain.

Why do we need to calculate the average atomic mass of isotopes of an element for computation?

An atom of an element has $2$ electrons in the $M$ shell, i.e., the third shell. What will be the atomic number of this element? Name this element. Find the valency of this element. Also, find the number of neutrons in the atom of this element (assume mass number is $24$).