Q: In this task, you are given a question and answer options for that question. Using this information, you have to classify each text into different topics: medicine, nursery, psychology, chemistry, pharmacology, biology.
Question: The alkali halides, MX:
Options: <0> They are solids that melt below 100C. <1> They form crystals of intense colors. <2> They can be obtained by reaction of the M2CO3 carbonates with the aqueous solutions of the HX hydrogen halides. <3> None of them can be found in nature. <4> They are liquid at room temperature.
A:
chemistry