You should select Router to connect the two groups of computers so that data communication can occur.
Routers are essential for the communication between two or more computers that are connected to a network. The primary function of routers is making connection between various networks and the data packets will be forwarded to the computers of same network of different networks.
It is a layer 3 device. This because the data that is contained in the layer 3 IP packet that contains the IP address of the destination to which the packet should be forwarded plays a very important role in making decisions related to the data packets forwarding. Thus a Router must be selected for connecting two groups of computer for data transfer and communication.