CG Board Class 10 Science Chapter 11 Solutions: Chemistry of Non-Metals (अधातुओं का रसायन) (2026-27)

(i) Water is made of two elements. Are these elements metals or non-metals?**

(ii) Is the gas which is essential to maintain life on earth a metal or non-metal?

(i) ?

• (i) Water (H_2O) is composed of Hydrogen (H) and Oxygen (O). Both hydrogen and oxygen are non-metals.
• (ii) The gas essential to maintain life on earth is Oxygen (O₂), which is a non-metal.
• (i) (H_2O) – (H) (O) **
• (ii) (O₂) , **

Metals are generally solids at room temperature, lustrous, malleable, ductile, and good conductors of heat and electricity. Hydrogen, oxygen, and nitrogen are gases at room temperature and normal pressure, non-lustrous, non-malleable, non-ductile, and poor conductors. Therefore, based on their physical state and lack of metallic properties, we determine that they are non-metals.

This is possible because of allotropy. Although both diamond and graphite consist entirely of carbon atoms, the arrangement of carbon atoms and the nature of chemical bonding between them are different

• In diamond, each carbon atom is covalently bonded to four other carbon atoms in a rigid three-dimensional tetrahedral network, making it extremely hard and transparent.
• In graphite, each carbon atom is bonded to three other carbon atoms in a hexagonal planar layer structure held together by weak Van der Waals forces, making it soft, slippery, and electrically conductive.

(a)**

• Metals: Element B (solid, ductile, conducts electricity).
• Non-metals: Elements A, C, and D.
• (b) Element ‘D’ is a solid that conducts electricity but is non-ductile (brittle). This exception matches graphite (an allotrope of carbon, which is a non-metal). The criteria to decide whether ‘D’ is a non-metal include its lack of ductility/malleability, brittleness, formation of acidic oxide (CO₂), and electronegative nature.

Allotropy is a property exhibited by elements occurring in different physical forms in the same state.

• Elements exhibiting allotropy: Carbon (C) (diamond, graphite, fullerenes) and Sulphur (S) (rhombic, monoclinic sulphur).
• CO₂, SO₂, C_4H₁₀, CH₄ are compounds, not elements, so they do not show allotropy.

Yes. In the modern periodic table

• Elements placed on the left side and center (Groups 1 to 12, except hydrogen) are metals.
• Elements placed along the diagonal zig-zag line (Boron, Silicon, Germanium, Arsenic, Antimony, Tellurium, Polonium) are metalloids.
• Elements placed on the extreme right side (Groups 14 to 18, along with Hydrogen in Group 1) are non-metals.

Yes, Hydrogen (H) is a non-metal that is placed on the extreme left side (Group 1, Period 1) of the periodic table because of its atomic number (1) and electronic configuration (1s¹).

Elements that exhibit physical and chemical properties intermediate between those of metals and non-metals are called metalloids or semi-metals. They lie along the diagonal zig-zag line separating metals and non-metals in the periodic table.

• Examples: Silicon (Si) and Germanium (Ge) (or Boron B, Arsenic As).

Gaseous elements were discovered much later than solid elements because

1. Gases are invisible, colorless, and odorless, making them difficult to detect visually or isolate in pure forms without specialized apparatus.
2. The techniques and equipment required to produce, trap, and collect gases over liquids (such as the pneumatic trough developed by Hales in the mid-18th century) were not available in ancient times.
3. Lack of early understanding of the gaseous state and its role in chemical reactions prevented early scientists from recognizing gases as distinct elements.

The elements of Group 18 (noble or inert gases like He, Ne, Ar, Kr, Xe, Rn) have completely filled outermost valence shells containing 8 electrons (octet completed, or duplet of 2 electrons in Helium). Because their electronic configurations are extremely stable, they have no tendency to gain, lose, or share electrons, making them chemically inert under normal conditions.

Yes. When sulphur burns in air, it forms sulphur dioxide gas (SO₂). When SO₂ is dissolved in water, it forms sulphurous acid (H_2SO₃). This solution turns moist blue litmus paper RED, while red litmus paper remains unchanged. This proves that sulphur dioxide is an acidic oxide.

S(s) + O₂(g) → SO₂(g)

SO₂(g) + H_2O(l) → H_2SO₃(aq) (Sulphurous acid)

1. Hydrochloric Acid (HCl): Hydrogen (H) and Chlorine (Cl).
2. Sulphuric Acid (H_2SO₄): Hydrogen (H), Sulphur (S), and Oxygen (O).
3. Nitric Acid (HNO₃): Hydrogen (H), Nitrogen (N), and Oxygen (O).
4. Carbonic Acid (H_2CO₃): Hydrogen (H), Carbon (C), and Oxygen (O).

Non-metals have 4, 5, 6, or 7 electrons in their outermost valence shell. Due to their relatively small atomic radii and high effective nuclear charge, non-metals have a strong tendency to gain electrons to achieve a stable octet noble gas configuration, forming negative ions (anions). Hence, non-metals are electronegative in nature.

1. Malleability/Brittleness Test: Hammer the solid element. If it flattens into a thin sheet without breaking, it is a metal. If it crumbles into powder (brittle), it is a non-metal.
2. Electrical Conductivity Test: Connect the element into a circuit with a battery and bulb. If the bulb glows (good conductor), it is a metal (except graphite exception). If it does not conduct electricity, it is a non-metal.
3. Nature of Oxide Test: Burn the element in air and dissolve its oxide in water. Test with litmus paper. If the solution turns red litmus blue (basic oxide), the element is a metal. If it turns blue litmus red (acidic oxide), the element is a non-metal.

Yes, all three names end with the suffix “-gen”. The suffix “-gen” is derived from the Greek word genes, which means ‘one which produces’ or ‘generator of’

• Hydro-gen: Water producer (hydro = water).
• Oxy-gen: Acid producer (oxy = acid).
• Nitro-gen: Nitre/saltpetre producer (nitro = nitre).

(i) Write the balanced chemical equation for the reaction between granulated zinc and hydrochloric acid.**

(ii) Activity-2 Question: How will you test that the gas collected by the displacement of water is hydrogen?

(i)

• (i) Balanced Chemical Equation:

Zn(s) + 2HCl(aq) → ZnCl₂(aq) + H₂(g)↑

• (ii) Test for Hydrogen Gas:

Bring a burning matchstick near the mouth of the test tube containing the gas. Hydrogen gas burns rapidly with a characteristic ‘pop’ sound, confirming its presence. (Precaution: Do not insert matchstick inside).

• (i) :
• (ii) :

1. H₂(g) + Br₂(g) → 2HBr(g) (Hydrogen bromide)
2. H₂(g) + F₂(g) → 2HF(g) (Hydrogen fluoride)

Bring a glowing wooden splint near the mouth of the test tube containing the collected gas. If the glowing splint immediately bursts into a bright flame, the gas is confirmed to be Oxygen (O₂), because oxygen supports combustion.

1. Reaction with Calcium (Ca):

Ca(s) + H₂(g) → CaH₂(s) (Calcium hydride)

1. Reaction with Lithium (Li):

2Li(s) + H₂(g) → 2LiH(s) (Lithium hydride)

1. Reaction with Aluminium (Al):

2Al(s) + 3H₂(g) → 2AlH₃(s) (Aluminium hydride)

Nitrogen gas (N₂)** is filled in packaged food containers and potato chip packets.

• Reason: Nitrogen provides an unreactive, inert atmosphere that replaces oxygen gas, preventing the oxidation (rancidity) of oils and fats present in food, thereby keeping the food fresh and crisp for a long time.

Oxygen gas is collected over water by the downward displacement of water because

1. Oxygen is only very slightly soluble (sparingly soluble) in water, so it does not dissolve significantly during collection.
2. It prevents oxygen from mixing with atmospheric air, yielding pure gas.

(i) The solution in water of which of the following will be acidic:**

• (a) Na_2O
• (b) CO₂
• (c) MgO
• (d) H_2O

(b) CO₂

Explanation: Carbon dioxide (CO₂) is a non-metallic oxide that dissolves in water to form carbonic acid (H_2CO₃), turning blue litmus red. Na_2O and MgO form basic solutions, while H_2O is neutral.

(i) The most electronegative element is …………….. (chlorine/ fluorine).**

(ii) Carbon is ………… (more/less) reactive as compared to oxygen.

(iii) Non-metals are found at the …………….(right/ left) side of the periodic table.

(iv) ……………….. (hydrogen/ nitrogen) gas is obtained when granulated zinc is reacted with dilute acid or alkali.

• (i) fluorine
• (ii) less
• (iii) right
• (iv) hydrogen

1. Hydrogen (H₂):

• Chloride: H₂(g) + Cl₂(g) → 2HCl(g)
• Oxide: 2H₂(g) + O₂(g) → 2H_2O(l)

1. Phosphorus (P₄):

• Chloride: P₄(s) + 6Cl₂(g) → 4PCl₃(l)
• Oxide: P₄(s) + 5O₂(g) → P_4O₁₀(s)

1. Sodium (Na):

• Chloride: 2Na(s) + Cl₂(g) → 2NaCl(s)
• Oxide: 4Na(s) + O₂(g) → 2Na_2O(s)

1. Magnesium (Mg):

• Chloride: Mg(s) + Cl₂(g) → MgCl₂(s)
• Oxide: 2Mg(s) + O₂(g) → 2MgO(s)

Nitrogen and hydrogen react to produce Ammonia gas (NH₃) via Haber’s Process.

• Balanced Chemical Equation:

N₂(g) + 3H₂(g) ⇌ [450°C-500°C, 200 atm / Fe catalyst, Mo promoter] 2NH₃(g)

• Reaction Conditions:

1. Temperature: 450°C – 500°C
2. Pressure: 200 atm (high pressure)
3. Catalyst: Finely divided Iron (Fe)
4. Promoter: Molybdenum (Mo) (increases catalyst efficiency)

Yes, we agree with this statement.** Hydrogen shows dual characteristics resembling both Group 1 alkali metals and Group 17 halogens

1. Resemblance with Group 1 (Alkali Metals):

• Electronic configuration: Contains 1 electron in the outermost shell (1s¹).
• Electropositive character: Can lose 1 electron to form a monovalent positive ion (H^+).
• Combines with non-metals (oxygen, sulphur, halogens) to form compounds like H_2O, H_2S, HCl.

1. Resemblance with Group 17 (Halogens):

• Requires 1 electron to complete its nearest noble gas configuration (He).
• Electronegative character: Can gain 1 electron to form a hydride ion (H^-), forming ionic hydrides (NaH, CaH₂) with active metals.
• Diatomic molecule: Exists as a diatomic gas (H₂), similar to F₂, Cl₂, Br₂.
• Non-metallic nature and high ionization energy.

Helium, neon, argon, krypton, xenon, and radon belong to Group 18 of the periodic table. They are called inert gases (or noble gases) because their outermost valence shells are completely filled with 8 electrons (octet completed; Helium has a duplet of 2 electrons). Due to this fully-filled stable electronic configuration, they have zero valency and no chemical affinity to gain, lose, or share electrons, remaining unreactive under normal conditions.

(a) Heat Production on Combustion:**

• Hydrogen gas has a very high calorific value and burns cleanly in oxygen to release immense thermal energy without emitting carbon pollutants

2H₂(g) + O₂(g) → 2H_2O(g) + Energy

• Industrial uses: Oxy-hydrogen flames (2800°C) are used for welding and cutting metals. Liquid hydrogen is used as high-energy rocket fuel and in fuel cells to generate electrical energy and heat.
• (b) Reaction with Vegetable Oils (Hydrogenation):
• Unsaturated organic compounds in vegetable oils contain carbon-carbon double bonds (C=C). When hydrogen gas is passed through liquid vegetable oil at 150°C-200°C in the presence of a Nickel (Ni) catalyst, the double bonds are converted into single bonds (C-C).
• Industrial process:

Unsaturated Vegetable Oil + H₂ → [Ni Catalyst / 150°C-200°C] Saturated Vegetable Fat (Vanaspati Ghee)

• This process is called Hydrogenation of Oils and is used to manufacture solid vegetable ghee from liquid oils.

When dark purple crystals of Potassium Permanganate (KMnO₄) are heated, thermal decomposition takes place, producing Potassium Manganate (K_2MnO₄), Manganese Dioxide (MnO₂), and Oxygen gas (O₂).

• Balanced Chemical Equation:

2KMnO₄(s) → [Δ] K_2MnO₄(s) + MnO₂(s) + O₂(g)↑

Identification:**

• Gas ‘A’: Hydrogen gas (H₂)
• Oxide ‘B’: Copper(II) Oxide / Cupric Oxide (CuO)
• Chemical Equations:

1. Formation of Gas ‘A’ (Hydrogen):

Zn(s) + 2HCl(aq) → ZnCl₂(aq) + H₂(g)↑ (Gas ‘A’)

1. Reduction of Oxide ‘B’ (Copper Oxide) by Gas ‘A’:

CuO(s) (Oxide ‘B’) + H₂(g) (Gas ‘A’) → [200°C] Cu(s) + H_2O(g)

Observation & Reason:**

• Moist Blue Litmus Paper turns RED.
• Moist Red Litmus Paper remains RED (no change).
• Reason: Burning sulphur powder produces Sulphur Dioxide gas (SO₂). When SO₂ reacts with moisture on the litmus paper, it forms Sulphurous acid (H_2SO₃). Being an acidic solution, it turns blue litmus paper red.
• Chemical Equations:

1. Combustion of Sulphur

S(s) + O₂(g) → SO₂(g)

1. Reaction of SO₂ with moisture

SO₂(g) + H_2O(l) → H_2SO₃(aq) (Sulphurous acid)

(a) This is due to the extremely low density** of hydrogen gas. Hydrogen is the lightest of all known elements and is much less dense than surrounding atmospheric air, providing upward buoyant force.

• (b) This is due to the extreme combustibility (flammability) of hydrogen gas. When hydrogen reacts rapidly with oxygen in the presence of a flame, a localized miniature explosion produces a characteristic ‘pop’ sound.

Identification:**

• Compound X: Water (H_2O) (Neutral liquid, pH = 7, used for drinking).
• Gas Y: Hydrogen gas (H₂) (Evolved at cathode, volume is double, highly combustible).
• Gas Z: Oxygen gas (O₂) (Evolved at anode, half volume of Y, supports combustion).
• Chemical Equation for Electrolysis:

2H_2O(l) → [Electrolysis / Acidified] 2H₂(g)↑ (Gas Y, Cathode) + O₂(g)↑ (Gas Z, Anode)

(Mole / Volume ratio of Y : Z = 2 : 1)