Which of the following pairs is mismatched?

$X$-rays of wavelength $0.140 \ nm$ are scattered from a block of carbon. What will be the wavelength of $X$-rays scattered at $90^{\circ}$ (in $nm$)?

Which among the following reactions will take place spontaneously?

$A$ parallel beam of light of wavelength $6000 \, \mathring{A}$ is diffracted by a single slit of width $0.3 \, \text{mm}$. The angular position of the first minima of the diffracted light is:

The number of unpaired electrons in a chromic ion $Cr^{3+}$ (atomic number $= 24$) is

$A$ ball at rest is dropped from a height of $12 ~m$. It loses $25 \%$ of its kinetic energy on striking the ground and bounces back to a height '$h$'. Then the value of '$h$' is: (in $~m$)