State whether the following statement is true or false:
Atoms combine in the ratio of small whole numbers to form compounds.

The ratio of the radii of a hydrogen atom and its nucleus is $\sim 10^5$. Assuming the atom and the nucleus to be spherical,
$(i)$ What will be the ratio of their sizes (volumes)?
$(ii)$ If the atom is represented by the planet Earth $(R_e = 6.4 \times 10^6 \, m)$,estimate the size of the nucleus.

The isotope of cobalt used in the treatment of cancer and iodine used in the treatment of goitre respectively are

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.

State whether the following statement is true or false:
The relative number and kinds of atoms are varying in a given compound.

$J. Chadwick$ discovered a subatomic particle which has no charge and has a mass nearly equal to that of a proton. Name the particle and give its location in the atom.