SSC
Halogens belong to which group of the modern periodic table?
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Answer: Option C — Group 17
Detailed Solution
The halogens are the elements of Group 17 (formerly Group VIIA) of the modern periodic table. They are fluorine (F), chlorine (Cl), bromine (Br), iodine (I), astatine (At) and the synthetic element tennessine (Ts). The name "halogen" comes from Greek words meaning "salt-former", because these elements react readily with metals to form salts, such as sodium chloride (common salt).
Properties of halogens:
They have seven electrons in their outermost shell (configuration ns² np⁵). They need only one more electron to complete an octet, so they are very reactive non-metals and form negative ions (anions) with a charge of –1.
They exist as diatomic molecules: F2, Cl2, Br2 and I2.
They are found in all three physical states at room temperature: fluorine (pale yellow gas) and chlorine (greenish-yellow gas) are gases, bromine (reddish-brown) is a liquid, and iodine (violet-black) is a solid that sublimes into violet vapour.
Reactivity decreases down the group: fluorine is the most reactive, and iodine is the least reactive of the common halogens. A more reactive halogen can displace a less reactive one from its salts.
Fluorine is the most electronegative element.
Uses of halogens:
- Fluorine: fluoride compounds in toothpaste to prevent tooth decay; Teflon (non-stick coating).
- Chlorine: disinfecting drinking water and swimming pools; making bleaching powder and PVC.
- Bromine: in flame retardants and earlier in photographic film (silver bromide).
- Iodine: tincture of iodine as an antiseptic; iodised salt to prevent goitre.
Other groups:
- Group 1: alkali metals (lithium, sodium, potassium).
- Group 2: alkaline earth metals (beryllium, magnesium, calcium).
- Group 16: chalcogens (oxygen, sulphur, selenium).
- Group 18: noble gases (helium, neon, argon), with full outer shells and very low reactivity.
- The modern periodic table, based on atomic number, has 18 groups (vertical columns) and 7 periods (horizontal rows), with 118 known elements.
Why not the other options?
- ✗Group 1 contains the alkali metals.
- ✗Group 16 contains the chalcogens (oxygen family).
- ✗Group 18 contains the noble gases.
Quick tip
Remember: Halogens = Group 17 (F, Cl, Br, I, At, Ts), "salt-formers", 7 valence electrons; bromine = only liquid non-metal; reactivity decreases down the group; Group 18 = noble gases.
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Periodic Classification of Elements — Preparation
This question tests your understanding of Periodic Classification of Elements, a key topic in the General Knowledge section. The detailed solution above uses a step-by-step approach to show the reasoning, and where available, a shortcut that helps you solve similar questions in under 90 seconds during the actual exam.
This topic covers the development of the periodic table (Dobereiner's triads, Newlands' law of octaves, Mendeleev's table and the modern periodic law), groups and periods, the properties of elements across the table, and noble gases, halogens and other important groups. Questions often ask who gave the modern periodic law (Henry Moseley, based on atomic number), which element is the most electronegative (fluorine), which metal is liquid at room temperature (mercury), and trends in atomic size and reactivity across periods and down groups. The modern periodic table has 18 groups and 7 periods. Practise the periodic table questions below, written in the style of the general awareness sections of exams such as SSC, banking, railways, CUET GAT, MAH CET and CLAT. Each question comes with a detailed explanation that adds related facts, so every question helps you revise more than one point.