Consider four atoms from the second period: lithium, beryllium boron carbon and nitrogen which of these element has the lowest electronegativity value?

Answer is: lithium.

Electronegativity (χ) is a property that describes the tendency of an atom to attract a shared pair of electrons.

Electronegativity increases from left to right across a period.  

Atoms with higher electronegativity attracts more electrons towards it, electrons are closer to that atom.

For example nitrogen has electronegativity approximately χ = 3 and lithium has χ = 1, so if they form bond, nitrogen will have negative and lithium positive charge.

water is used to store them because it would keep the radiation from getting out in the open and causing harm to the workers

answer is: naturally occurring solid, inorganic compound or element is mineral.

minerals usually have crystalline form, that means than crystal constituents (atoms, molecules or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions.

for example magnetite is a mineral of iron oxide (fe₂o₃).

calcite is a carbonate mineral and the most stable polymorph of calcium carbonate (caco₃).

dolomite is an   carbonate mineral composed of calcium magnesium carbonate (camg(co₃)₂).