Chemistry help wanted!?

a. Ar (Z = 18) : 1s² 2s² 2d⁶ 3s² 3p⁶
b. Cl (Z = 17) : 1s² 2s² 2d⁶ 3s² 3p⁵
c. S (Z = 16) : 1s² 2s² 2d⁶ 3s² 3p⁴
d. P³⁻ (Z = 15) : 1s² 2s² 2d⁶ 3s² 3p⁶

The answers : b and c

Electron configuration.....

1s2, 2s2 2p6, 3s2 3p6

This is the electron configuration for argon, an inert gas. There are several ions which are isoelectronic with argon. That is, they have the same number of electrons in the same configuration.

Ions which are isoelectronic with argon: S^2-, Cl^-, K+, Ca2+, Sc^3+, Ti^4+.
Ions in aqueous solution extend from occasionally -2 (in very basic solutions) to sometimes +4, but not beyond.

For instance, there is no P^3- ion. Phosphorous can have an oxidation state of -3, but not an ionic charge of -3. It takes far too much energy to push three negatively charged electrons onto a phosphorous atom. There is simply too much repulsion. Please don't confuse the actual charge on at atom in a compound with its oxidation state. For instance, in Na3P the bonds have have about 33% ionic character (67% covalent character). So, despite the network structure of Na3P, the bonds are significantly more covalent, than ionic. Bonds fall along a bonding continuum with the hypothetical "ionic" and "covalent" bonds at each end. These are called "ideal bonds." But real bonds lie along the continuum and have characteristics of both ideal bonds. It is estimated that P in Na3P has an actual charge of about -1, and sodium atoms have a charge of about +0.33.

Unlike compounds like NaCl with bonds with high ionic character (about 70% ionic) which ionizes to form Na+ and Cl- ions in solution, Na3P does not ionize in solution, but reacts with water to make NaOH(aq) and PH3 gas (phosphine).

Argon has the electron configuration that you gave, neither chlorine nor sulfur do, but sulfide ion and chloride ion do. And "phosphide ion" hypothetically has that electron configuration, but it doesn't exist.

1s2
2s2
2p6
3s2
3p6

2 + 2 + 6 + 2 + 6 = 18
This is element number 18. This is the number protons in the nucleus of the atom. The element is argon. It is the last element in row three of periodic table.

3s2p6 is part of the electron configuration that indicates that Argon has eight electrons in its outer shell. This is called an octet. All of the elements in column 18 of the periodic table have this type of electron configuration. They are called noble gases. I hope this is helpful for you.

You need to follow your periodic table. The first two columns on the left are the s columns. the transition metals are the p. the last column is d, and the floating two rows is f. What I don't understand is that you re asking which one could not have the configuration. The reason that configurations are used in chemistry is because they are unique to every element, so the configuration can only be assigned to that one element. For example, the configuration above belongs to rubidium, so I am not quite sure what you are trying to ask here