Write the source of ultraviolet waves.

Which of the following can be used in cancer treatment?

Given below are some famous numbers associated with electromagnetic radiations in different contexts in physics. State the part of the electromagnetic spectrum to which each belongs.
$(a)$ $21 \; cm$ (wavelength emitted by atomic hydrogen in interstellar space).
$(b)$ $1057 \; MHz$ (frequency of radiation arising from two close energy levels in hydrogen; known as Lamb shift).
$(c)$ $2.7 \; K$ (temperature associated with the isotropic radiation filling all space; thought to be a relic of the 'big-bang' origin of the universe).
$(d)$ $5890 \; \mathring{A} - 5896 \; \mathring{A}$ (double lines of sodium).
$(e)$ $14.4 \; keV$ (energy of a particular transition in $^{57}Fe$ nucleus associated with a famous high-resolution spectroscopic method, Mossbauer spectroscopy).

$TV$ waves range from . . . . . .

Arrange the following in the ascending order of wavelength $(\lambda) :$
$(A)$ Microwaves $(\lambda_1)$
$(B)$ Ultraviolet rays $(\lambda_2)$
$(C)$ Infrared rays $(\lambda_3)$
$(D)$ $X-$rays $(\lambda_4)$
Choose the most appropriate answer from the options given below $:-$

Which is the correct ascending order of wavelengths?