Question

Which of the following elements is less reactive than the others?

Answer 1

Answer: The correct answer is Bromine (Br).

Explanation:

All the given elements are non-metals as they gain electrons to attain stability.

Reactivity of non-metals is defined as the tendency of the atom to gain electrons.

The reactivity of non-metals decreases as we move from top to bottom in a group. As, the electrons get added up in the new shell. The electron in the outermost orbital gets far away from the nucleus. And hence, the electron will be difficult to gain because the attraction between the nucleus and the added electron is not that strong. Thus, the chemical reactivity of non-metals decreases.

For the given options:

Bromine (Br) belongs to Group 17 and Period 4 of the periodic table.

Oxygen (O) belongs to Group 16 and Period 2 of the periodic table.

Selenium (Se) belongs to Group 16 and Period 4 of the periodic table.

Sulfur (S) belongs to Group 16 and Period 3 of the periodic table.

Hence, bromine is least reactive element from the given ones.

Answer 2

Bromine. 

Oxygen, selenium, and sulfur are all in group 16 and have 6 valence electrons. Bromine is in group 17 and has 7 valence electrons. The closer to 8 (a full, stable octet) you get, the less likely the element is to react.