Question

Which of the following elements could be described as least reactive, relative to the other three answer choices? Why so?

Au
Ca
Fe
Mg

Answer 1

Gold without a question. (Au).

Explanation:

Gold has the highest electo negativity of the four positive atoms.
A positive atoms is more reactive as the electo negativity is lower.
This makes Magnesium the most reactive.

Positive atoms need to lose electrons in order to react. The smaller the atom and the fewer electrons the atom needs to lose make it more reactive. Magnesium and Calcium both need to lose two electrons but Magnesium is number 12 in the second period and Calcium is number 20 in the third period so Calcium is less reactive than Magnesium but more reactive than Iron

Iron number 26 has 8 valance electrons. For Iron to lose all 8 electrons is almost impossible. Iron typically loses either both of the s orbital electrons or both of the s orbital and 1 of the d electrons. Losing 1 of the d electrons gives Iron a pseudo stable half filled d shell. Iron is in the fourth shell which makes it smaller and more reactive than gold