The figure that is not a direct manifestation of the quantum nature of atoms is:

Supposing the electron is present in the $4^{th}$ energy level of $H$ atom. When the electron returns to the ground state,the possible transitions would be:

The angular momentum of an electron in the $7^{th}$ Bohr orbit of a hydrogen atom is given by:

In astronomical observations,signals observed from the distant stars are generally weak. If the photon detector receives a total of $3.15 \times 10^{-18} \, J$ from the radiations of $600 \, nm$,calculate the number of photons received by the detector.

The radius of stationary state $(n=2)$ of hydrogen atom is $x \ pm$. The radius of stationary state $(n=3)$ of $He^{+}$ ion (in $pm$) is

Which of the following activities can be compared to the concept of quantisation?