The radius of a nucleus is given by $r_0 A^{1 / 3}$, where $r_0=1.3 \times 10^{-15} \,m$ and $A$ is the mass number of the nucleus. The lead nucleus has $A=206$. The electrostatic force between two protons in this nucleus is approximately ................ $N$

In a Geiger-Marsden experiment, what is the distance of closest approach to the nucleus of a $7.7 \;MeV$ $\alpha -$particle before it comes momentarily to rest and reverses its direction?

The following diagram indicates the energy levels of a certain atom when the system moves from $2E$ level to $E$, emitting a photon of wavelength $\lambda $. The wavelength of photon produced during its transition from $\frac{4E}{3}$ level to $E$ is

Assertion $(A)$ : The magnetic moment $(\mu)$ of an electron revolving around the nucleus decreases with increasing principle quantum number $(n)$.

Reason $(R)$ : Magnetic moment of the revolving electron, $\mu \propto n$.

For principal quantum number $n = 3$, the possible values of orbital quantum number $‘l’$ are

In third orbit of hydrogen atom, de Broglie wavelength of electron is $\lambda $ then radius of third orbit is