Which of the following elements is less reactive than the others? bromine (br) oxygen (o) selenium (se) sulfur (s)

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.

the old alchemists made significant contributions to science even though there starting premises were off a bit. their conclusions after failure would steer them into better directions for investigation. science is no more than close observation and the initial mistakes result in rethinking and retrying experiments.

the enthalpy of formation of water is given as -285.8kj/mol, which states that the enthalpy of formation is negative.

negative enthalpy of formation indicates that the heat is released during the reaction process. the heat is released from reaction to the surroundings the enthalpy is expressed with a negative sign with the energy given out in the reaction process.

the formation of water takes place by giving out heat which is -285.8 kj/mol.