The correct answer is: C. inert gas
The electronic configuration of an element tells us how many electrons are in each shell and subshell of that element. The number of electrons in the outermost shell determines the chemical properties of an element. Elements with a full outermost shell are very stable and do not react easily. These elements are called inert gases.
The electronic configuration of element Z is (2, 8, 8). This means that element Z has 2 electrons in its first shell, 8 electrons in its second shell, and 8 electrons in its third shell. The third shell is the outermost shell of element Z, and it has 8 electrons. This means that element Z is an inert gas.
The other options are incorrect because they do not describe the properties of element Z. Option A, non-metal, is incorrect because non-metals do not have a full outermost shell. Option B, metalloid, is incorrect because metalloids have properties that are in between metals and non-metals. Option D, metal, is incorrect because metals have a full outermost shell and are therefore very reactive.