Question

The most reactive element in the halogen group is ………….
A. Astatine
B. Iodine
C. Chlorine
D. Fluorine

Answer 1

Hint: Recall all the properties for an element that affect the reactivity of the element and check how it varies in a group on going up or going down.

Complete step by step answer:

The halogens are located on the left of the noble gases on the periodic table. These five toxic, non-metallic elements make up Group 17 of the periodic table and consist of: fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At).
Although astatine is radioactive and only has short-lived isotopes, it behaves similar to iodine and is often included in the halogen group.
Halogens are highly reactive, and as such can be harmful or lethal to biological organisms in sufficient quantities. This high reactivity is due to the high electronegativity of the atoms due to their high effective nuclear charge.
Because the halogen elements have seven valence electrons, they only require one additional electron to form a full octet. This characteristic makes them more reactive than other non-metal groups.
Fluorine is one of the most reactive elements. It reacts with otherwise inert materials such as glass, and it forms compounds with the heavier noble gases. It is a corrosive and highly toxic gas. Fluorine’s reactivity means that once it does react with something, it bonds so strongly that the resulting molecule is inert and non-reactive. Thus fluorine must be handled with substances like the inert organofluorine compound Teflon.

Hence, the correct option is D.

Note: Fluorine gas is extremely toxic; breathing in fluorine at a concentration of 25 parts per million is potentially lethal.
Hydrofluoric acid is also toxic, being able to penetrate skin and cause highly painful burns. In addition, fluoride anions are toxic, but not as toxic as pure fluorine.
Fluoride can be lethal in amounts of 5 to 10 grams. Prolonged consumption of fluoride above concentrations of 1.5 mg/L is associated with a risk of dental fluorosis, an aesthetic condition of the teeth.