Consider radio waves $(r),$ visible light $(v),$ infrared $($i$),$ X rays $($ x $),$ and ultraviolet $(u).$ In order of increasing frequency, they are:

$r,i,v,x,u$

$r,i,v,u,x$

i$,$ r$,$ v$,$ u$,$ x

$x,u,v,i,r$

$r,v,i,x,u$