It depends. many of the websites i see answering the questions are all over the place, but good luck.
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.
Sodium bicarbonate (or baking soda) will cause both exothermic and endothermic reactions when added to water. It becomes either unstable or stable carbonic acid, which will eventually become CO2. The reaction would be exothermic is when H2CO3 (Carbonic Acid unstable) is formed and endothermic is when CO2 is.
