The correct relationships between unit cell edge length '\( a \)' and radius of sphere '\( r \)' for face-centred and body–centred cubic structures respectively are:
\( 2\sqrt{2}\, r = a \) and \( 4r = \sqrt{3}\, a \)
\( r = 2\sqrt{2}\, a \) and \( \sqrt{3}\, r = 4a \)
\( r = 2\sqrt{2}\, a \) and \( 4r = \sqrt{3}\, a \)
\( 2\sqrt{2}\, r = a \) and \( \sqrt{3}\, r = 4a \)
