Answer: is A
Reason: because the rest are common...
Gas to solid ( a ) is correct i think
Group 1a elements (the first column on the left side of the Periodic table) always release one electron to form positive ions with a charge of +1. Group 7a nonmetals (the <em>second to the last </em>column on the right side- the rightmost column are the noble gases) always desire to gain one electron to form negative ions with a charge of -1.
Since their charges are equal and opposite, they will always combine in a 1:1 ratio.
