Which of the following is true about semi-conductors
-neither free eletrons nor hoes are considered charge carriers in a semi-conductor
-exposing a crysal of a semiconductor to heat or light starts displacing valence electrons which then move throughout the crystal
-a material is classified as a semiconductor if its resistance to the flow of electric current is too low to permit it to be called a conductor

The statement that is true about semi conductors is this: A MATERIAL IS CLASSIFIED AS A SEMI CONDUCTOR IF ITS RESISTANCE TO THE FLOW OF ELECTRIC CURRENT IS TOO LOW TO PERMIT IT TO BE CALLED A CONDUCTOR.

Semi conductors refers to those materials that can conductor electricity only under suitable conditions, their resistance to the flow of electricity lies between that of conductors and non conductors. Semi conductors are usually used in some electric circuits because the flow of electricity through them can easily be controlled. Examples of semi conductors are silicon, germanium and selenium.

"among the transition metal elements, manganese and zinc have a slight lowering of electronegativities. the reason behind this is that the nuclear charges of these elements are slightly weaker than the other transition metal elements due to the way their valence electrons are filled up. both manganese and zinc have their valence electrons filled up to the 4th shell with 1 pair of electrons (4s2) completely occupying it. although the electrons in the 3rd shell (3d) are yet to be paired since the outer most shell is filled up, the ability of the nucleus to attract electrons is lessened. hence,   the electronegativity (or the ability to attract electrons) is lessened."

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.