Write the charge and mass of an electron.

State reasons for the following statements:
$(i)$ Some elements possess fractional atomic mass.
$(ii)$ Isotopes of an element have similar chemical properties.
$(iii)$ Noble gases are inert.

Identify the $Mg^{2+}$ ion from the figures,where $n$ and $p$ represent the number of neutrons and protons,respectively.

Sulphur dioxide $(SO_{2})$ is a colourless,pungent-smelling gas and is a major air pollutant.
$(a)$ Write the electronic configuration of its constituent elements,sulphur and oxygen.
(Given: $_{16}^{32}S, _{8}^{16}O)$
$(b)$ Write the valency of sulphur and oxygen.
$(c)$ Are sulphur and oxygen isotopes of the same element? Explain your answer.

In what way is the Rutherford's atomic model different from that of Thomson's atomic model?

State two main postulates of Thomson's model of an atom.