Answer:- Bromine
Explanations:- 7th group elements are known as halogens and these are fluorine, chlorine, bromine, iodine and astatine. At room temperature, fluorine and chlorine are gases, bromine is liquid, iodine is solid and astatine is a post transition metal.
In question, it says the element is liquid at room temperature, so it would be bromine since only bromine is liquid at room temperature.
Atomic number of Bromine is 35 and mass number is around 80. So number of neutrons = 80 - 35 = 45
It is also confirmed from neutrons calculations that the element is bromine.