The ion of an element has $3$ positive charges. The mass number of the atom is $27$ and the number of neutrons is $14$. What is the number of electrons in the ion?

$(a)$ Both helium and beryllium have two electrons in their valence shells. Helium is a noble gas whereas beryllium is a metal. Justify.
$(b)$ Hydrogen exists in three isotopic forms. Why are the isotopes of hydrogen chemically alike?

List applications of any three isotopes in various fields.

Write any two observations which support the fact that atoms are divisible.

In response to a question,a student stated that in an atom,the number of protons is greater than the number of neutrons,which in turn is greater than the number of electrons. Do you agree with the statement? Justify your answer.

Write two differences between isobars and isotopes.