What is the correct electron configuration for magnesium? ( use periodic table)
a) 1s22s22p5
b) 1s22s22p6
c) 1s22s22p63s2
d) 1s22s22p63s23p2

The answer is c)

Explanation:

The neutral atoms have the same number of protons (positive charge) and electrons (negative charge). So in the periodic table the atomic number shows the number of protons and electrons.

Magnesium has an atomic number of 12, so it has 12 electrons. Electronic configuration shows the location of the electrons around the atom nucleus. To know its electronic configuration we will need to use  the order of fill (the chart in the image), which indicates how the electrons are placed into the orbitals based on the order of their energy. The lowest energy orbitals (such as ) will be occupied first.

So according to this Magnesium electronic configuration will be as 2+2+6+2=12 electrons. The superscript of each orbital is the amount of electrons that occupied it.

answer is: c. the experiment shows that the red substance experienced a chemical change.

this is chemical change (chemical reaction), because two new substances are formed (metalig liquid and gas), the atoms are rearranged and the reaction is followed by an energy change.

this is example of chemical decomposition.

chemical decomposition (analysis) is the separation of a single chemical compound into its two or more elemental parts or to simpler compounds.  

chemical decomposition is opposite of chemical synthesis.