What is an ozone hole?

Which of the following can be used in cancer treatment?

Write the range of frequencies for radio waves and $FM$ band radio.

$A$ monochromatic source of light operating at $15 \text{ kW}$ emits $2.5 \times 10^{22} \text{ photons/s}$. The region of an electromagnetic spectrum to which the emitted electromagnetic radiation belongs to . . . . . . . (Take $h = 6.6 \times 10^{-34} \text{ J}\cdot\text{s}$ and $c = 3 \times 10^8 \text{ m/s}$).

If wavelengths of visible rays, microwaves, and $X$-rays are $\lambda_v$, $\lambda_m$, and $\lambda_x$ respectively, then which of the following relations is correct?

Which of the following are not electromagnetic waves?