As I know, the elements which exist as gas in standard temperature and pressure (STP) is Fluorine and Chlorine. Now since the question asks about which group on the periodic table, we refer to the group of Fluorine and Chlorine. So the answer is:
Group 17 (VIIA)
Answer: The group which has two elements existing in gaseous state is Group 17.
Explanation:
Elements are distributed in 7 periods and 18 groups. Groups are the vertical columns and periods are the horizontal rows.
Elements belongs to groups 1 to 14 contain all the elements that exist as solids except for Mercury (Group 12, Period 6) which exist as liquid.
Elements that belong to Group 15 and 16 have one element each which exist as gases. Rest all the elements exist as solid. In Group 15, the element that exist as gas is Nitrogen and in group 16, the element is Oxygen.
Elements that belong to Group 17 have two elements that exist as gases which are Fluorine and Chlorine. Bromine gas exist as liquid and iodine exist as solid.
Elements that belong to Group 18 are all gases and are hence known as noble gases.
Thus, the group which has two elements existing in gaseous state is Group 17.
