The of a wave is the density of the medium’s particles at the compression of the wave.

The given question is incomplete, the complete question is:

The of a wave is the density of the medium’s particles at the compression of the wave.

The given blank can be filled with amplitude.

Explanation:

A longitudinal wave that travels in the form of rarefaction and compression is termed as the sound wave. Rarefaction refers to the point where the particles are positioned far away from each other, on the other hand, compression refers to the point where the particles are adjacent to each other.  

Amplitude of the wave is the maximum displacement from the position of equilibrium. It is the density of the particles of the medium at the compression of the wave.  

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.

colorless gas, exhibiting a blue glow when placed in an electric field

b) solid

its a type of rock