Which of the following elements is NOT a noble gas?

Noble gases are a group of elements found in Group 18 of the periodic table, known for their lack of reactivity due to having a complete valence shell of electrons. Helium, krypton, and xenon are all noble gases, which means they possess the characteristic properties of being colorless, odorless, and exhibiting very low chemical reactivity under standard conditions.

Calcium, on the other hand, is an alkaline earth metal located in Group 2 of the periodic table. It has two electrons in its outermost shell, which makes it reactive, especially with water and acids. This reactivity contrasts sharply with the inert nature of the noble gases. Therefore, identifying calcium as not being a noble gas is correct because it does not share the same electronic configuration or properties that define noble gases.