<P> Most molecules are far too small to be seen with the naked eye, but there are exceptions . DNA, a macromolecule, can reach macroscopic sizes, as can molecules of many polymers . Molecules commonly used as building blocks for organic synthesis have a dimension of a few angstroms (Å) to several dozen Å, or around one billionth of a meter . Single molecules cannot usually be observed by light (as noted above), but small molecules and even the outlines of individual atoms may be traced in some circumstances by use of an atomic force microscope . Some of the largest molecules are macromolecules or supermolecules . </P> <P> The smallest molecule is the diatomic hydrogen (H), with a bond length of 0.74 Å . </P> <P> Effective molecular radius is the size a molecule displays in solution . The table of permselectivity for different substances contains examples . </P> <P> The chemical formula for a molecule uses one line of chemical element symbols, numbers, and sometimes also other symbols, such as parentheses, dashes, brackets, and plus (+) and minus (−) signs . These are limited to one typographic line of symbols, which may include subscripts and superscripts . </P>

Molecule 3 is formed as a result of