The number of electrons in the outermost '$L$' shell of an atom is $5$.
$(a)$ Write its electronic configuration.
$(b)$ What is its valency and why?

$(a)$ Write two drawbacks of Rutherford's model of an atom.
$(b)$ State Bohr's postulates to overcome the drawbacks of Rutherford's model.

$(a)$ Explain Bohr$-$Bury rules for the distribution of electrons into different shells.
$(b)$ Write the electronic configuration of an atom of sulphur. Also,draw a schematic diagram of its atom showing the distribution of electrons in its shells.

Rutherford's alpha $(\alpha)$ particles scattering experiment resulted in the discovery of:

The electron distribution in an aluminium atom is

The average atomic mass of a sample of an element $y$ is $35.5 \,u$. What are the percentages of isotopes $_{17}^{37}y$ and $_{17}^{35}y$ in the sample?