State occurence of group-17 elements.

Explanation

(i) Fluorine : Fluorine is present mainly as insoluble fluorides such as fluorspar (`CaF_2`), cryolite (`Na_3AlF_`6) and fluoroapatite [`3Ca_3(PO_4)_2. CaF_2`] and small quantities are present in soil, river water plants and bones and teeth of animals.
(ii) Chlorine : Sea water mainly contains 2.5% by mass of sodium chlorides. The deposits of dried up seas contain these compounds, e.g., sodium chloride (NaCl), carnallite (KCl-`MgCl_2-6H_2O`).
(iii) Bromine and iodine : Apart from sodium chloride, sea water also contains bromides and iodides of potassium, magnesium and calcium.
Ex. : NaBr, KBr, `MgBr_2` etc. while iodine is mainly obtained as iodates (NaI03). certain marine life contain iodine in their systems, various seaweeds, for example, contain upto 0.5% of iodine and chile saltpetre contains upto 0.2% of sodium iodate.
(iv) Tennessine : Tennessine is a synthetic radioactive element. (At. Mass = 294). Only small amount of the element could be prepared as its half life is in milliseconds only.
In the periodic table, the Group-17 only contains the element in all three states of matter. All are reactive non-metals.
Fluorine is used in toothpaste and refrigerant gases, chlorine for bleach and chemical warfare, bromine in fire retardant material while iodine in antiseptics.