Task: Question Answering
Input (English): Question: The alkali halides, MX: 
 Options:  <1> They are solids that melt below 100ºC. <2> They form crystals of intense colors. <3> They can be obtained by reaction of the M2CO3 carbonates with the aqueous solutions of the HX hydrogen halides. <4> None of them can be found in nature. <5> They are liquid at room temperature.
Output (English): 3