What are the periodic table group number and a representative element for X in the ionic compound Sr₃X₂?

• A. group number of X: 2A
  representative element: Mg
• B. group number of X: 5A
  representative element: N
• C. group number of X: 3A
  representative element: Al
• D. group number of X: 6A
  representative element: S

Answer: (B)