The value of Planck's constant is $6.63 \times 10^{-34} \ J \ s$. The speed of light is $3 \times 10^{17} \ nm \ s^{-1}$. Which value is closest to the wavelength in nanometers of a quantum of light with a frequency of $6 \times 10^{18} \ s^{-1}$?

The energy required to release $1$ electron from $He^{+}$ is $............$ $eV$.

The maximum energy is present in any electron at

Positronium consists of an electron and a positron (a particle which has the same mass as an electron,but opposite charge) orbiting round their common centre of mass. Calculate the value of the Rydberg constant for this system.

Which one of the following about an electron occupying the $1s$ orbital in a hydrogen atom is incorrect? (The Bohr radius is represented by $a_0$)

Given below are two statements: one is labelled as Assertion $A$ and the other is labelled as Reason $R$:
Assertion $A$: In the photoelectric effect,the electrons are ejected from the metal surface as soon as the beam of light of frequency greater than threshold frequency strikes the surface.
Reason $R$: When the photon of any energy strikes an electron in the atom,transfer of energy from the photon to the electron takes place.
In the light of the above statements,choose the most appropriate answer from the options given below: