Define the bond length.

Explanation

Bond length is defined as the equilibrium distance between the nuclei of two bonded atoms in a molecule.
Bond lengths are expressed in terms of Angstrom `(10^(-10) m)` or picometer `(10^(-12) m)` and are measured by spectroscopic X-ray diffractions and electron-diffraction techniques.
In an ionic compound, the bond length is the sum of the ionic radii of the constituting atoms `(d=r_(+)+r_(-))`. In a covalent compound, it is the sum of their covalent radii `(d=r_(A)+r_(B))`.