Diamond has lesser density than platinum . So , if we take equal mass of both , the volume of mass of platinum will be far less .
The density of both diamond and platinum are more than water so both of them will be drowned in water completely . They will not float . On being drowned , platinum will displace lesser volume of water because of its less volume . So volume change in case of platinum mass will be far less . The volume change for diamond will be more because of its bigger size.
