Answer:
Group 1 (or IA)
Explanation:
If element X is a halogen, then it belongs to the group 17 (or VIIA, under a different notation).
For each extra unit of atomic number, the group number increases by 1. That means that the X+1 element would belong to the group 18 (or VIIIA). <em>The X+2 element would thus belong in the group 1 </em>(or IA) one period higher (higher as in numeric value, not as in position in the periodic table).
Answer D, because it's acid
