Define international system of units , where does the system originate

The diagin dilutepage 6 of 12a6a5(a)fluorine, chlorine, bromine and iodine are placed in the same group of theperiodic table.state the common name used to describe elements in this group.(i)state the group in which the elements are placed and explain whythey are placed in that group.(ii)which of the above named elements is a solid at roomtemperature and pressure?