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

$A$ $150 \ W$ bulb emits light of wavelength $6600 \ \mathring{A}$ and only $8 \%$ of the energy is emitted as light. How many light photons are emitted by the bulb per second?

The ionisation energy of a certain element is $1540 \ kJ \ mol^{-1}$. When the atoms of this element are in the first excited state,the ionisation energy is only $300 \ kJ \ mol^{-1}$. Determine the region of the electromagnetic wave spectrum in which the light is emitted during a transition from the first excited state to the ground state.

The energy of an electron in the $3^{rd}$ orbit of a hydrogenic atom is $-E$. The energy of an electron in the first orbit will be

Write down the postulates of Bohr's model for the hydrogen atom.

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