Task: Question Answering
Input (English): Context: Halogens are highly reactive nonmetallic elements in group 17 of the periodic table. As you can see in the periodic table 1.1, the halogens include the elements fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). All of them are relatively common on Earth except for astatine. Astatine is radioactive and rapidly decays to other, more stable elements. As a result, it is one of the least common elements on Earth. Q: Based on their position in the periodic table from the Figure 1.1, how many valence electrons do you think halogens have? A: The number of valence electrons starts at one for elements in group 1. It then increases by one from left to right across each period (row) of the periodic table for groups 1-2 and 13-18 (numbered 3-0 in the periodic table above.) Therefore, halogens have seven valence electrons. The halogens are among the most reactive of all elements, although reactivity declines from the top to the bottom of the halogen group. Because all halogens have seven valence electrons, they are eager to gain one more electron. Doing so gives them a full outer energy level, which is the most stable arrangement of electrons. Halogens often combine with alkali metals in group 1 of the periodic table. Alkali metals have just one valence electron, which they are equally eager to donate. Reactions involving halogens, especially halogens near the top of the group, may be explosive. You can see some examples in the video below. (Warning: Dont try any of these reactions at home!) Click image to the left or use the URL below. URL: The halogen group is quite diverse. It includes elements that occur in three different states of matter at room temperature. Fluorine and chlorine are gases, bromine is a liquid, and iodine and astatine are solids. Halogens also vary in color, as you can see in the Figure 1.2. Fluorine and chlorine are green, bromine is red, and iodine and astatine are nearly black. Like other nonmetals, halogens cannot conduct electricity or heat. Compared with most other elements, halogens have relatively low melting and boiling points. Most halogens have a variety of important uses. A few are described in the Figure 1.3. Q: Can you relate some of these uses of halogens to the properties of these elements? A: The ability of halogens to kill germs and bleach clothes relates to their highly reactive nature. 
 Question: halogens tend to form compounds with elements in group
Output (English): 1.