Answer: B. Magnesium, strontium, radium, barium
Step-by-step explanation:
Elements are distributed in groups and periods in a periodic table.
Elements that belong to same groups will show similar chemical properties because they have same number of valence electrons.
Magnesium (Mg) , Strontium (Sr) , Radium (Ra) and Barium (Ba) are elements which belong to Group 2. They have 12, 38, 88 and 56 electrons respectively and contain 2 valence electrons each and need one electron to complete their octet.
The chemical reactivity of elements is governed by the valence electrons present in the element and thus they are alike in physical and chemical properties.