* Alkali metals are found in Group 1 of the periodic table.

* Neutrons are found in the nucleus of an atom, along with protons.

* Atomic mass is approximately equal to the number of protons + neutrons.

Let's look at the alkali metals and their typical atomic masses:

* Lithium (Li): Atomic mass ~ 7 (3 protons + 4 neutrons)

* Sodium (Na): Atomic mass ~ 23 (11 protons + 12 neutrons)

* Potassium (K): Atomic mass ~ 39 (19 protons + 20 neutrons)

* Rubidium (Rb): Atomic mass ~ 85 (37 protons + 48 neutrons)

* Cesium (Cs): Atomic mass ~ 133 (55 protons + 78 neutrons)

* Francium (Fr): Atomic mass ~ 223 (87 protons + 136 neutrons)

Therefore, the alkali metal with 12 neutrons is Sodium (Na).