Which of the following electron configurations describes an element that is a noble gas?
a. 1s22s22p4

b. [ne]2s22p2

c. [ar] 3s1

d. 1s22s22p6

The answer to your question is: letter D.

Explanation:

Noble gases are located in group VIIIA of the periodic table, this means that they have 8 eight electrons in their outermost shell.

Due to this characteristic, they are stable and do not react with other elements.

a. 1s22s22p4    The outermost shell of this electron configuration has 6 electrons, then this element has 6 electrons not 8. This configuration is of an element of the group VIA.

b. [Ne]2s22p2  The outermost shell of this element has 4 electrons, so this is not the configuration of a noble gas.

c. [Ar] 3s1  This element only has one electron in its outermost shell, so this is the electron configuration of an alkaline metal.

d. 1s22s22p6 This element has 8 electrons in its outermost shell, so this is the electron configuration of a noble gas.

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explanation:

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2fe + 3h2so4 -> fe2(so4)3 + 3h2

it is necessary to balance equations in order to get the proper amount of reactants as well as products in order not to make a miscalculation.

you cannot change the subscripts as that would change the substance itself. for instance, diatomic elements such as h2 only have the subscript two when a gas. another example would be so4, if you were to change the subscript, the element would no longer be sulfate.

we change the coefficients instead as that only changes the number of molecules rather than the substance itself.

hope this !