Infrared Spectroscopy:
Infrared spectroscopy is a technique that measures the absorption of infrared radiation by molecules. It detects the stretching, bending, and vibrating motions of the atoms within a molecule. When a molecule absorbs infrared radiation, it undergoes a change in its vibrational energy levels.

Microwave Spectroscopy:
Microwave spectroscopy is a technique used to study the rotational energy levels of molecules. It measures the absorption of microwave radiation by molecules, which corresponds to the energy differences between different rotational states. It is not suitable for determining vibrational stretching frequencies.

Raman Spectroscopy:
Raman spectroscopy is a technique that measures the inelastic scattering of light by molecules. When light interacts with a molecule, it can undergo a change in energy due to the scattering process. Raman spectroscopy provides information about the vibrational and rotational energy levels of molecules.

Rotational Raman Spectroscopy:
Rotational Raman spectroscopy is a variant of Raman spectroscopy that specifically focuses on the rotational energy levels of molecules. It measures the changes in the rotational energy levels of a molecule when it scatters light. It is not suitable for determining vibrational stretching frequencies.

Vibrational Stretching Frequency of N2:
The correct answer to the question is option 'C', Raman spectroscopy. This is because Raman spectroscopy can provide information about the vibrational energy levels of a molecule, which is what is needed to determine the vibrational stretching frequency of N2.

In the case of N2, it is a diatomic molecule consisting of two nitrogen atoms. The vibrational stretching frequency corresponds to the energy required to stretch the bond between the atoms. Raman spectroscopy can detect the changes in the vibrational energy levels of N2 when it scatters light. By analyzing the Raman spectra, the vibrational stretching frequency of N2 can be determined.

In conclusion, Raman spectroscopy is the appropriate technique for determining the vibrational stretching frequency of N2 because it provides information about the vibrational energy levels of molecules. Infrared spectroscopy is also a suitable technique for studying vibrational energy levels, but it is not the correct answer in this case. Microwave spectroscopy and rotational Raman spectroscopy are not suitable for determining vibrational stretching frequencies.