Find out the valency of the atoms represented by the Fig. $(a)$ and $(b)$.

With the help of a labelled diagram,describe in brief the Rutherford's alpha particle scattering experiment. Write any three important conclusions drawn from the experiment.

State whether the following statement is true or false:
The relative atomic masses of all elements have been found with respect to an atom of oxygen-$16$.

Dalton's atomic theory successfully explained which of the following laws?
$(i)$ Law of conservation of mass
$(ii)$ Law of constant composition
$(iii)$ Law of radioactivity
$(iv)$ Law of multiple proportion

In the Thomson's model of atom,which of the following statements are correct?
$(i)$ The mass of the atom is assumed to be uniformly distributed over the atom.
$(ii)$ The positive charge is assumed to be uniformly distributed over the atom.
$(iii)$ The electrons are uniformly distributed in the positively charged sphere.
$(iv)$ The electrons attract each other to stabilize the atom.

The number of electrons in an element $X$ is $15$ and the number of neutrons is $16$. Which of the following is the correct representation of the element?