Question

The radioactive element present in the first group of s-block is ______.
A. Radium
B. Francium
C. Caesium
D. Barium

Answer 1

Hint: Try to recall that a radioactive element is one where the nucleus is unstable. Generally, the last elements of each group in the modern periodic table are radioactive due to high atomic number.

Complete step by step answer:
> The radioactive element present in the first group of s-block is the second most electropositive element, behind only caesium. It has atomic number 87 and is represented with the symbol Fr.
> Out of the above four options, francium is the radioactive element present in the first group of s-block elements. It is an alkali metal and most of the chemical properties of francium resemble caesium.
> Francium is extremely radioactive and its most stable isotope is francium-233. It has a half-life of only 22 minutes. The isotopes of francium decays quickly into astatine, radium and radon.
> Francium-233 is found in uranium minerals via alpha decay of the actinium-227. Also, francium is the least electronegative of all the elements of all the known elements till date.
> Radium is also a radioactive element and it belongs to the second group (alkaline earth metal) of s-block.
> Caesium and Barium are not the radioactive elements.

So, the correct option is (B).

Note:
Don’t confuse between Radium and Francium because both are radioactive elements but the major difference is Radium belongs to the second group of the periodic table and Francium belongs to the first group.