Answer:
They are all located in the same horizontal row or period.
Explanation:
In the periodic table the elements are arranged according to their increasing atomic number.The elements those contain low atomic number are placed in the first row such as hydrogen and helium. similarly the radioactive elements those have high atomic number are placed in 7th or 8th row.
All the elements of a family in the peroidic table have common features are located in same horizontal row or period.For example fluorine,chlorine,bromine and iodine are placed in VII B class of periodic table as all of them are electronegative in nature.
