The only helpful bacterium found in humans is found in the stomach?

hmmm

Explanation:

I'm pretty sure it's either bifidobacteria or lactobacillus

Possibly Probiotics

they are very helpful to the  human gut

Or the most 2 helpful bacteria are Lactobacillus and Bifidobacteria

Explanation:

organisms are more likely to be more preserved in mud than sand because mud is moist and wet, while sand is very dry.

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.