What is the packet of energy called?

The ratio of kinetic energies of photoelectrons emitted from a metal by light of frequencies $v_1$ and $v_2$ is $1 : 2$. The threshold frequency of the metal will be:

Which of the following transitions has the minimum wavelength?

$A$ certain transition in the hydrogen spectrum from an excited state in one or more steps gives rise to a total of $10$ lines. The number of lines lying in the visible spectrum is:

Light of frequency $1.6 \times 10^{16} \ Hz$ falling on a metal plate emits electrons that have double the kinetic energy compared to the kinetic energy of electrons emitted when light of frequency $1.0 \times 10^{16} \ Hz$ falls on the same plate. The threshold frequency $(v_0)$ of the metal in $Hz$ is:

The ratio of the difference between the $1^{st}$ and $2^{nd}$ Bohr orbits energy to the difference between the $2^{nd}$ and $3^{rd}$ Bohr orbits energy is: