To identify the unknown compound "X" using mass spectrometry data, we need to follow these steps:1. Determine the molecular formula of "X" based on the molecular ion peak.2. Analyze the fragment peaks to deduce the possible structure of "X".Step 1: Determine the molecular formula of "X"The molecular ion peak is observed at m/z 120, which indicates the molecular weight of "X" is 120. The most common elements in organic compounds are carbon, hydrogen, oxygen, and nitrogen. We can use the nitrogen rule and the degrees of unsaturation to help narrow down the possibilities.The nitrogen rule states that if a compound has an odd mass, it must have an odd number of nitrogen atoms. Since the molecular weight of "X" is 120 an even number , it must have an even number of nitrogen atoms 0 or 2 .The degrees of unsaturation can be calculated using the formula: U = C - H/2 + N/2 + 1, where U is the degrees of unsaturation, C is the number of carbon atoms, H is the number of hydrogen atoms, and N is the number of nitrogen atoms. The degrees of unsaturation can indicate the presence of double bonds, triple bonds, or rings in the molecule.Considering the molecular weight of 120 and the possible presence of carbon, hydrogen, oxygen, and nitrogen, a reasonable molecular formula for "X" could be C8H8O 120.15 g/mol .Step 2: Analyze the fragment peaksNow, let's analyze the fragment peaks and their relative intensities:m/z 105 40% : Loss of a methyl group CH3, 15 g/mol from the molecular ion peak suggests the presence of a methyl group in the molecule.m/z 92 15% : Loss of CO 28 g/mol from the molecular ion peak suggests the presence of a carbonyl group C=O in the molecule.m/z 77 10% : Loss of a propyl group C3H7, 43 g/mol from the molecular ion peak suggests the presence of a propyl group in the molecule.m/z 65 5% : Loss of a phenyl group C6H5, 77 g/mol from the molecular ion peak suggests the presence of a phenyl group in the molecule.Based on the fragment peaks and the molecular formula C8H8O, the structural formula of "X" can be deduced as 1-phenyl-1-propanone also known as propiophenone :C6H5-C O -CH2-CH3In conclusion, the molecular formula of "X" is C8H8O, and its structural formula is 1-phenyl-1-propanone.