Which of the following events may occur when ir radiation is absorbed?

a. relative nuclear spins of nucleii with non-zero io's are changed.
b. bonding electrons are promoted to higher energy molecular orbitals.
c. more intense ir absorptions occur for those bonds having greater dipole moment changes with bond lengthening in a vibration.
d. vibrational amplitudes of bonds are increased.
e. intra-molecular bond angles are changed.

c. More intense IR absorption occur for those bonds having greater dipole moment changes with bond lengthening in a vibration.

Explanation:

When the molecules is exposed to the infrared radiation, the sample molecules absorb the radiation of wavelengths (specific to molecule) which causes change in the dipole moment of the sample molecules. The vibrational energy levels of the sample molecules consequently transfer from the ground state to the excited state.  

Frequency of absorption peak is determined by vibrational energy gap.

Intensity of absorption peaks is related to change of dipole moment and possibility of transition of the energy levels.  

Thus, by analyzing infrared spectrum,abundant structure information of the molecule can be known.

Hence, the correct answer to the question is

c. More intense IR absorption occur for those bonds having greater dipole moment changes with bond lengthening in a vibration.

i think the answer is a, hope this is right, that would be my best guess.