The third peak in the X-ray diffraction pattern of a face-centered cubic crystal is at $2 \theta$ value of $45^{\circ}$, where $2 \theta$ is the angle between the incident and reflected rays.
The wavelength of the monochromatic X-ray beam is $1.54 A^{\circ}$. Considering first-order reflection, the lattice parameter of the crystal is $A^{\circ}$.
$\text{(Round off to two decimal places)}$
