The frequency of the stretching vibration of a bond in IR spectroscopy depends on what two quantities?

A) the stiffness of the bond and the electronegativity of the atoms
B) the electronegativity of the atoms and the nuclear charges of the atoms
C) the masses of the atoms and the stiffness of the bond
D) the nuclear charges of the atoms and the atomic radii
E) the electronegativity of the atoms and the masses of the atoms

The frequency of the stretching vibration of a bond in IR spectroscopy depends on the masses of the atoms and the stiffness of the bond. The frequency of a bond's stretching vibration is proportional to the square root of the bond stiffness and inversely proportional to the square root of the reduced mass of the two atoms in the bond. Hence, the two quantities that affect the frequency of the stretching vibration are the masses of the atoms and the stiffness of the bond.