In which group of the modern periodic table are halogens placed?

The correct answer is D, 17th. The halogens are placed in Group 17 of the modern periodic table. This family has five members - fluorine, chlorine, bromine, iodine and astatine. Every halogen atom carries seven electrons in its outermost shell, so it needs just one more electron to complete its octet. That single gap makes the halogens the most reactive non-metals, and it is why they combine so readily with metals to form salts; the word halogen itself means salt-former. Reactivity falls down the group, fluorine being the most reactive and iodine the least. A is wrong because group 16 is the chalcogen family of oxygen and sulphur, whose atoms carry six valence electrons. B is wrong because group 18 holds the noble gases such as helium, neon and argon, whose outermost shells are already complete, so they stay almost inert. C is wrong because group 1 is the alkali metals such as sodium and potassium, which carry one valence electron and lose it easily. Exam tip: group 16 chalcogens, group 17 halogens, group 18 noble gases.