Metallic radii of some transition elements are given below. Which of these elements will have highest density?

Element	$Fe$	$Co$	$Ni$	$Cu$
Metallic radii/pm	126	125	125	128

On moving left to right along period, metallic radius decreases while mass increases. Decrease in metallic radius coupled with increase in atomic mass results in increase in density of metal. Hence Cu will have highest density.