Which of these techniques gives us molecular weight information from which we can work out a molecular formula?Group of answer choicesmass spectrometryIR spectroscopy1H NMR spectroscopycombustion analysisUV/Vis spectroscopy

The technique that gives us molecular weight information from which we can work out a molecular formula is Mass Spectrometry.

Mass spectrometry is a technique that ionizes chemical species and sorts the ions based on their mass-to-charge ratio. The mass spectrum produced provides information about the molecular weight of the compound and its structure. This information can be used to determine the molecular formula of the compound.

The other techniques listed (IR spectroscopy, 1H NMR spectroscopy, combustion analysis, UV/Vis spectroscopy) provide different types of information:

• IR spectroscopy provides information about the functional groups present in a molecule.
• 1H NMR spectroscopy provides information about the number and type of hydrogen atoms in a molecule.
• Combustion analysis provides information about the amount of carbon, hydrogen, and oxygen in a compound, which can be used to determine the empirical formula, but not the molecular formula without additional information.
• UV/Vis spectroscopy provides information about the electronic structure of a molecule and can be used to study things like conjugated systems or transition metal complexes.