Answer :
The answer is (1). Hf is solid, Hg is liquid, and He is gaseous. You can look up a periodic table online that shows each element's state of matter at STP.
Answer: Option (1) is the correct answer.
Explanation:
STP means standard temperature and pressure where temperature is 273.15 K and pressure is 1 bar or 0.98 atm.
It is known that only bromine (Br) and mercury (Hg) are in liquid form at STP. Whereas noble gases like He, Ne, Ar etc are gases in nature.
Hence, given elements are differentiated as follows.
HF - solid, Hg - liquid, and He - gas
Ba - solid, [tex]Br_{2}[/tex] - liquid, and B - solid
Cr - solid, [tex]Br_{2}[/tex] - gas, and C - solid
Se - solid, Sn - solid, and Sr - solid
Thus, we can conclude that list of elements contains a solid, a liquid, and a gas is HF, Hg, He.
