The nuclear and atomic radii of these elements keep on increasing as we move down the group. This happens because of the addition of an extra energy level. They have the minimal atomic radii compared to the other elements in the related periods. This can be attributed to the fact that their atomic charge is quite powerful.

• Physical state: The group 17 elements are found in diverse physical states. For example, Fluorine and Chlorine are gases. On the other hand, Bromine is a liquid and Iodine is solid.
• Colour: These elements have a variety of colours. For example, while Fluorine is pale yellow in colour, Iodine is dark violet in colour.
• Solubility: Florine and Chlorine are soluble in water. On the other hand, Bromine and Iodine are very less soluble in water.
• Melting and boiling points: Melting and boiling points of these elements increase as we move down the group from Fluorine to Iodine. Thus, Fluorine has the lowest boiling and melting points.

1. Electronic configuration-The general electronic configuration for this group is ns²np⁵

• Fluorine (F) [He]2s²,2p⁵
• Chlorine (Cl) [Ne]3s²,3p⁵
• Bromine(Br)[Ar]3d¹⁰4s²4p⁵
• Iodine (I)[Kr]4d^10,5s²,5p⁴
• Astatine (At) [Xe]4f¹⁴,5d¹⁰,6s²,6p⁴

The members of group 17 are:

• Fluorine(F) - 9
• Chlorine(Cl) - 17 
• Bromine(Br) - 35
• Iodine (I) - 53
• Astatine (At) - 85

The members of group 17 are:

• Fluorine(F)
• Chlorine(Cl)
• Bromine(Br)
• Iodine (I)
• Astatine (At)

The halogens are the elements that form group 17 of the periodic table. They are reactive nonmetals and include fluorine, chlorine, bromine, and iodine.

Nascent hydrogen is most powerful reducing agent than ordinary hydrogen because nascent hydrogen is in atomic state and atoms are more active than molecules, nascent hydrogen is evolved in small bubbles containing the gas under great pressure, nascent hydrogen is activated by the energy liberated in the reaction in which it is formed, so the nascent hydrogen becomes more energized and active.

1. In the laboratory, sulphur dioxide is prepared by the reaction of metallic sulphite or a metallic bisulphite with dilute acid. For example, a reaction between the dilute sulphuric acid and sodium sulphite will result in the formation of SO₂.

Na₂SO₃ + H₂SO₄ → Na₂SO₄ + H₂O + SO₂

2. Commercially it is obtained as a by-product released from the roasting of sulphide ores. The gas obtained is dried, liquefied and then stored in steel cylinders.

4FeS₂ (s) + 11 O₂ (g) →2Fe₂O₃ (s) + 8SO₂ (g)

The space in a molecule in which the probability of finding an electron is maximum can be calculated using the molecular orbital function. Molecular orbitals are basically mathematical functions that describe the wave nature of electrons in a given molecule.

These orbitals can be constructed via the combination of hybridized orbitals or atomic orbitals from each atom belonging to the specific molecule. Molecular orbitals provide a great model via the molecular orbital theory to demonstrate the bonding of molecules.

The temperature at which electrical resistivity of the material suddenly drops of zero and the material changes from normal conductor to a super conductor is called the Transition temperature or critical temperature T C ​ .

Sulphur forms numerous allotropes, but let us study the two most important allotropes of sulphur-

yellow rhombic sulphur (α-sulphur) and the monoclinic (β-sulphur). The most interesting feature is their thermal stability, the allotropes of sulphur are inter-convertible i.e. rhombic sulphur when heated above 369K gives monoclinic sulphur. 

Rhombic sulphur (α-sulphur)

Rhombic sulphur is crystalline in nature and has octahedral shape. On heating the solution of roll sulphur in CS2 we get rhombic sulphur. It is yellow with a melting point of 385.8K and specific gravity 2.06. Rhombic sulphur cannot be dissolved in water but can be dissolved in benzene, ether, alcohol etc.

Monoclinic sulphur (β-sulphur)

When we take a dish and melt rhombic sulphur in that dish we obtain monoclinic sulphur after cooling it. In this process we make two holes in the crust and pour out the remaining liquid. After this we get colourless needle-shaped crystals of β-sulphur when the crust is removed.

• Diamond: It is extremely hard, transparent crystal, with the carbon atoms arranged in a tetrahedral lattice. This allotrope of carbon is a poor electrical conductor and an excellent thermal conductor.
• Lonsdaleite: These are also called hexagonal diamond.
• Graphene: It is the basic structural element of other allotropes, nanotubes, charcoal, and fullerenes.
• Q-carbon: These carbon allotropes are ferromagnetic, tough, and brilliant crystal structure that is harder and brighter than diamonds.
• Graphite: It is a soft, black, flaky solid, a moderate electrical conductor. The C atoms are bonded in flat hexagonal lattices (graphene), which are then layered in sheets.
• Linear acetylenic carbon (Carbyne)
• Amorphous carbon
• Fullerenes, including Buckminsterfullerene, also known as “buckyballs”, such as C60.
• Carbon nanotubes: Allotropes of carbon with a cylindrical nanostructure.

• Ozone used at water treatment plants without filtration systems.
• Ozone may also be formed by commonly used equipment such as photocopiers, laser printers, and other electrical devices.
• In medicine, by limiting the effects of bacteria, viruses, fungi, yeast, and protozoa, ozone therapy is used to disinfect and treat diseases.
• Several ozone-depleting compounds possess properties that make them good refrigerants that is, they can efficiently transfer heat from one location to another.

Resonance structures are sets of Lewis structures that describe the delocalization of electrons in a polyatomic ion or a molecule.

In many cases, a single Lewis structure fails to explain the bonding in a molecule/polyatomic ion due to the presence of partial charges and fractional bonds in it. In such cases, resonance structures are used to describe chemical bonding.

Resonance structure of ozone (O)₃

Ozone performs an essential function by forming a ozone layer which shields the surface of the earth from the entry of UV rays from the sun.

"Nascent" just means newly-formed. A single oxygen atom, not yet bonded to anything.

1. Neutral Oxide is one which neither has an acidic characteristic or a basic one.

• It is a colourless, odourless diatomic gas and paramagnetic in nature.
• Oxygen is highly reactive non-metal.
• This diatomic gas is a strong oxidizing gas.
2SO2 + O2 → 2SO3
• It is second most electronegative element after fluorine.
• Dioxygen reacts with metals, non-metals to give oxides of the respective element.
2Ca + O2 → 2CaO

Fractional distillation is a type of distillation which involves the separation of miscible liquids. The process involves repeated distillations and condensations and the mixture is usually separated into component parts. The separation happens when the mixture is heated at a certain temperature where fractions of the mixture start to vaporize.

KMnO₄ when heated to 473 K, readily decomposes giving oxygen. At red heat, potassium permanganate decomposes into potassium manganate (K2MnO3) and oxygen.

The world depicted on the class-room walls differs from the world of the slum children in the sense that the pictures on the walls mean progress, prosperity and well-being. But the children of slum children live in a troubled state. They are devoid of education, money and other necessities of life.(i) The walls of the slum class room were decorated with donations from various people. They depict fabulous cities that shine in the morning sun and beautiful Tyralese vales. But the world of the slum children is the world they see outside their class room windows, the dark allies roofed with the burning sun. Their world is full of dirty rubbish heaps.

(ii) According to Keats the beautiful things of earth makes man love love earth and the life in it, in spite of problems and miseries.

(iii) Aunt Jennifer was in perpetual fear of her husband. But she yearned to be fearless and free. The prancing tigers in her embroidery represent her unfulfilled aspirations.

(iv) The poet was extremely aware of her mother's advancing age and feared that she may die soon as she is getting old. So when she left her in the airport she fixed an artificial smile on her lips and said "See you soon, Amma". But at the same time she had the fear that she may not see her Amma when she comes next.