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

List applications of any three isotopes in various fields.

An ion $Y^{3-}$ contains $18$ electrons and $16$ neutrons. Calculate the atomic number and mass number of the element $Y$. Name the element $Y$.

In a sample of ethyl ethanoate $(CH_3COOC_2H_5)$,the two oxygen atoms have the same number of electrons but different number of neutrons. Which of the following is the correct reason for it?

$(a)$ 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.

Is it possible for the atom of an element to have one electron,one proton,and no neutron? If so,name the element.