Reactive metals are those that readily lose electrons to achieve a noble gas configuration. The outermost shell of these metals will have a low number of electrons, which means that they are loosely held and can be easily removed. Common examples include the alkali metals (Group 1) and the alkaline earth metals (Group 2) in the periodic table.

Here are the outer electron configurations of some common elements and their reactivity:

Helium (He): 1s² (noble gas, non-reactive)

Lithium (Li): 2s¹ (alkali metal, highly reactive)

Sodium (Na): 3s¹ (alkali metal, highly reactive)

Magnesium (Mg): 3s² (alkaline earth metal, moderately reactive)

Aluminum (Al): 3s²3p¹ (post-transition metal, less reactive)

Iron (Fe): 3d⁶4s² (transition metal, moderately reactive)

Copper (Cu): 3d¹⁰4s¹ (transition metal, less reactive)

Bromine (Br): 4s²4p⁵ (halogen, highly reactive)

Iodine (I): 5s²5p⁵ (halogen, moderately reactive)

Xenon (Xe): 5s²5p⁶ (noble gas, non-reactive)

Based on this, the outer electron configuration that would be expected to belong to a reactive metal is:

A) ns¹ (one electron in the outermost shell), like Lithium (Li) or Sodium (Na).