As per given figure A ,   B and C are the first, second and third excited energy levels of hydrogen…

As per given figure $A, B$ and $C$ are the first, second and third excited energy levels of hydrogen atom respectively. If the ratio of the two wavelengths$\left(i.e. \frac{{\lambda }_1}{{\lambda }_2}\right)$ is $\frac{7}{4n}$, then the value of $n$ will be