Question

Among the group seventeen members. Radioactivity is present in: -
A.Fluorine
B.Astatine
C.Iodine
D.Chlorine

Answer 1

Hint: The group seventeen elements are called halogens. These elements have just one unpaired electron in their outermost orbital and also their size is smaller than their previous groups.

Complete answer:
The group seventeen elements are called halogens. These elements have just one unpaired electron in their outermost orbital and also their size is smaller than their previous groups. These elements have highest ionisation enthalpy, this value keeps on diminishing as we go down the group. This is due to the increase in the size of the nucleus. Electrons gain enthalpy of these elements and keep on decreasing down the group. These elements exhibit the highest electronegativity values. This is due to the least distance of the nucleus from the surrounding which is the least as compared to their previous periods.
All these halogens have high oxidising power. The fluorine has the highest oxidising power. Once it was believed that oxygen was the most electronegative but halogens or fluorine are the only elements in Presence of which the oxygen supports a positive oxidation state.
Halogens react very readily with hydrogen. Hydrogen being the most electropositive, readily gives away the electron therefore resulting in the formation of very high acidic compounds. $HF$ is the strongest acid of them all?
Among this astatine is the heaviest known halogen. The total amount of astatine in the earth's crust at any particular time is less than $30gm$. It has a very short lifetime which makes it hazardous to human health. It is the least reactive of the halogens.
Astatine is the radioactive element among them.

Note:
Radioactive elements have very high demand and on the contrary are their availability. These elements have very less knife span making them hazardous to humans and therefore as important for humans.