What element forms an ion with an electronic configuration of 1s22s22p63s23p6 (or [Ar]) and a –2 charge? Give the symbol for the element
element symbol

Sulfur (S)

Explanation: An ion with the same electron configuration as Ar has the same number of electrons as Ar. Because the ion has a −2 charge, a neutral atom of the element has 2 fewer electrons than Ar. The number of electrons in a neutral atom is equal to the atomic number. When sulfur, S, gains two electrons, it has the same configuration as Ar. Sulfur has an electron configuration of 1s²2s²2p⁶3s²3p⁴   (1s2 2s2 2p6 3s2 3p4) meaning it is 2 away from having a noble gas configuration (its charge is −2). So the ion's configuration is 1s²2s²2p⁶3s²3p⁶     (1s2 2s2 2p6 3s2 3p6).  Alternately, this can be written as [Ne]3s²3p⁶ or [Ar].

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it can be observed without changing the identity of the object.

it depends on what substance you're talking about as well as many other factors. in quantum mechanics, the observation of particles affects the observers ability to measure certain properties. for example: you can know the velocity of a particle, but you can't know it's position; or you can know it's position, but not it's velocity. it's like trying to find out where a grain of sand is by throwing other grains of sand at it. once you find out where it is, it's been moved. it's also like trying to find an answer to the question of whether or not a tree falling in a forest makes a sound if nobody is there to hear it. paradoxically, the only way to find out is to be there and hear it.