In which of the following transition will the wavelength be minimum:

The correct option is C $\text{n =3 to n =1}$
The energy released for a transition is given by,
$\Delta E=13.6Z^2(\frac{1}{n_1^2}-\frac{1}{n_2^2})eV$
Where,
$n_1\to$ Lower energy state
$n_2\to$ higher energy state
So , from the given options the energy associated will be highest for the transition $\text{n =3 to n =1}$
Again, $E=h\nu =h\frac{c}{\lambda }$
So energy $E$ is inversely proportional to the wavelength ($\lambda$).
So the minimum wavelength will be associated with the transition $\text{n =3 to n =1}$ only.