What are the horizontal (from left to right) parts of the periodic table called?

rows
periods
families

The correct answer is periods. See the explanation below, please.

Explanation:

The horizontal lines in the periodic table are called periods (ranging from 1 to 7) and vertical lines (ranging from 1 to 18).

The period that an element belongs to coincides with the last electronic layer of the element (that compound in period 3 will have 2 electronic layers).

alkaline metals are lithium, sodium, rubidium, potassium, cesium and francium.

alkali metals have electronegativity from 0.7 to 1, lowest in periodic table of elements, which means that alkali metals (i group in periodic table) has positive oxidation number in compounds.

electronegativity is a chemical property that describes the tendency of an atom to attract a shared pair of electrons towards itself.

alkaline metals (far left in main group) have lowest ionizations energy and easy remove valence electrons,

for example, potassium is the alkali metal and has a single valence electron in the outer electron shell.

electron configuration of potassium is: ₁₉k 1s²2s²2p⁶3s²3p⁶4s¹.

they can not exist alone in nature, because they are very reactive.

it's c (engineer's do their work with mechanical stuff not on any living being)