In each of the following atoms or ions, electron jumps from n = 2 to n = 1. The wavelength of radiation emitted will be minimum for

The wavelength will be minimum for the emission having maximum energy, out the given particles the deexcitation in double ionized lithium will have maximum energy. $\left(∆\mathrm{E}\propto {\mathrm{Z}}^2\right)$

So doubly ionized lithium will have minimum wavelength.