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

The wavelength of a spectral line emitted by a hydrogen atom in the Lyman series is $\frac{16}{15 R} \ cm$. What is the value of $n_2$? $(R = \text{Rydberg constant})$

The ratio of the radius of the first excited state of $Li^{2+}$ to the radius of the second excited state of $H$ is ....

In a hydrogen atom,if an electron transitions from an $n$-th orbit to the ground state,and the total number of spectral lines observed is $10$,then the value of $n$ is:

In an emission spectrum,the transitions $n_2 \to n_1$,$n_3 \to n_2$,$n_4 \to n_3$,and $n_5 \to n_4$ emit energies $E_1, E_2, E_3$,and $E_4$ respectively. What is the increasing order of these energies?

Energy levels $A, B, C$ of a certain atom correspond to increasing values of energy, $i.e.,$ $E_A < E_B < E_C$. If $\lambda_1, \lambda_2$ and $\lambda_3$ are the wavelengths of radiations corresponding to the transitions $C$ to $B$, $B$ to $A$ and $C$ to $A$ respectively, which of the following statements is correct?