A diffraction grating has $45,000$ slits$/$cm$.$ What is the distance between adjacent slits?

$1\mathrm{.}0$ cm

$2\mathrm{.}2$ cm

$2\mathrm{.}2{10}^{-5}cm$

None of these.

X$-$rays diffract from crystalline matter because...

The wavelength of the X $-$rays is comparable to the atomic spacing in matter.

The wavelength of the $x-$rays is much shorter than the atomic spacing in matter.

The wavelength of the X $-$rays is much larger than the atomic spacing in matter.