In XRD scan on Cu $($FCC structure$),$ a peak showed up at $2\backslash$theta $=43\mathrm{.}2$ degree. If the interplanar spacing $($nm$)$ of this peak $($dhkl$)$ is $0\mathrm{.}209$ nm$.1)$ Determine the wavelength of X$-$ray $($nm$)$ when the order of reflection is $1.2)$What is the planar density $($mmol$/$m$2)$ of $(001)$ plane of Cu$?$