Answer:
M is Li, X is boron, and Q is oxygen. MX is LiB, lithium bromide. QX is BO, boron oxide (not Body Odor).
Explanation: The atomic masses don't match exactly with those listed in the periodic table. Boron, Oxygen, and Lithium come the closest.
Lithium reacts with bromine since it happily donates it's single 2s electron to bromine's 4p orbital to fill bromine's 4s and 4p valence orbitals to go from 7 to 8 valence electrons, it's happy state.
Boron reacts with oxygen to form B2O3, which I'll happily write as O=BOB=O, since my name is Bob. This is more complex, but both elements want to move electrons around in order to reach a more stable electron configuration. Boron has 3 valence electrons and oxygen has 6. So each oxygen needs 2 electrons to fill it's outer shell and boron is happy to lose it's 3 valence electrons to reach an outer shell equiovalent to helium. So 2 borons contribute a total of 6 electrons, and the 3 oxygens have room for a total of 6 electrons to fill their outer shell.
