The approximate ratio of the speed of light in vacuum to that of an electron in the first Bohr orbit of hydrogen atom is (in $: 1$)

The ratio of the area covered by the second orbital to the first orbital is

The ratio of the radius of the second orbit of hydrogen to the third orbit of $Li^{+2}$ is .... ($H$ atomic number = $1, Li$ atomic number = $3$)

What is the wavelength of light emitted when the electron in a hydrogen atom undergoes transition from an energy level with $n=4$ to an energy level with $n=2$ (in $nm$)?

Assertion : For Balmer series of hydrogen spectrum,the value $n_1 = 2$ and $n_2 = 3, 4, 5...$
Reason : The value of $n$ for a line in Balmer series of hydrogen spectrum having the highest wavelength is $4$ and $6$.

Time taken for an electron to complete one revolution in the Bohr orbit of hydrogen atom is