From kinetic theory, tell the dimension of an atom.

If in nature there may not be an element for which the principal quantum number $n > 4,$ then the total possible number of elements will be

The diagram below shows the lowest four energy levels for an electron in a hypothetical atom.The electron is excited to the $-1\,eV$ level of the atom and transitions to the lowest energy state by emitting only two photons. Which of the following energies could not belong to either of the photons ? .....$eV$

A beam of fast moving alpha particles were directed towards a thin film of gold. The parts $A',\;B'$ and $C'$of the transmitted and reflected beams corresponding to the incident parts $A, B$ and $C$ of the beam, are shown in the adjoining diagram. The number of alpha particles in

The diagram shows the path of four $\alpha  - $ particles of the same energy being scattered by the nucleus of an atom simultaneously. Which of these are/is not physically possible

Consider the following statements:

$I$. All isotopes of an element have the same number of neutrons.

$II$. Only one isotope of an element can be stable and non-radioactive.

$III$. All elements have isotopes.

$IV$. All isotopes of carbon can form chemical compounds with oxygen-$16$.

Choose the correct option regarding an isotope.