Which electron configuration could represent a strontium atom in an excited state?

From the periodic table, we know that Strontium has 38 electrons. Therefore, any option that does not add up to 38 should be eliminated. This makes option A and C wrong.

Strontium as you may know is an alkali metal; and alkali metals are very reactive elements. The normal configuration of strontium is 2 – 8 – 18 – 8 – 2 but when excited, one of the eight electrons bump up to the valence shell making the configuration become 2 – 8 – 18 – 7 – 3.

The only difference between option B and option D is that either one more or one less electron in the outer two shells. Option B is the excited state and option D is the natural (ground) state of Strontium.

Each element has an electron configuration that corresponds to its proton number. These electrons are responsible for the reactivity of the element. Strontium is an alkali metal and alkali metal and is one of the most reactive elements on earth. It has a normal configuration with two valence electrons in its outer shell. However, as the element is excited, one of the eight electrons bump into the valence shell.

Ultimately, the new configuration becomes 2-8-18-7-3. This is how it binds to other atoms and creates strong compounds. It has many shells in its atoms, so the outer electrons are further away from the nucleus. This is what allows this phenomenon to occur.