(2)

Gamma rays have smallest wavelength.

(4)

The wavelength of AM radio waves is ${10}^2\text{m}$. The wavelength of microwaves ranges between ${10}^{-3}\text{m}$ to ${10}^{-1}\text{m}$. Infrared radiations wavelength lines between $4\times {10}^{-7}\text{m}$ to $7\times {10}^{-3}\text{m}$. X-rays wavelength ranges from ${10}^{-8}\text{m}$ to ${10}^{-12}\text{m}$. 

(3)

As  $\lambda =\frac{hc}{E}$

where the symbols have their usual meanings.

Here, $E=15\text{keV}=15\times {10}^3\text{eV}$ and $hc=1240\text{eV}$ $\mathrm{nm}$

$\therefore$  $\lambda =\frac{1240 \text{eV nm}}{15\times {10}^3 \text{eV}}=0.083$ $\text{nm}$

As the wavelength range of X-rays is from 1 nm to ${10}^{-3}$ nm, so this wavelength belongs to X-rays.