What causes hydrogen bonding? bonding of a covalently bonded hydrogen atom with an unshared electron pair

motion of electrons

attraction between ions

sharing of electron pairs between two adjacent hydrogen atoms

the tendency of some atoms in molecules to attract electrons more than their accompanying atom.

Explanation:

a compound is a molecule made of atoms from different elements.

a. by the combination of an unlimited number of elements

space exploration has led to the development and technological improvement of many everyday items. (if this answer is wrong i will find the right answer) : )