Class 9 Chemistry Second Terminal Christmas Exam Answer Key 2025

CLASS 9 CHEMISTRY - SECOND TERM EXAM ANSWER KEY

Summative Assessment - Term II (2025-26)

Exam: Chemistry

Class: IX

Maximum Score: 40

Time: 1½ Hours

Questions 1-4 (Each 1 mark)

1

Assertion (A): The atomic number of potassium is 19 and its electron configuration is 2, 8, 8, 1.
Reason (R): The maximum number of electrons that can be accommodated in the outermost shell of any atom is 8.
Which among the following is correct?

Answer: (D) A is false, but R is true.

Explanation: Potassium (Z=19) actually has electron configuration 2,8,8,1, but R is generally true for stable octet configuration, though there are exceptions for atoms with d and f orbitals.

2

Some statements related to the characteristics of ionic compounds are given. Which is correct?

Answer: (C) Statement 1 is incorrect, but 2, 3, and 4 are correct.

Explanation: Ionic compounds are generally soluble in water (Statement 1 is wrong). They are hard, have high melting/boiling points, and conduct electricity only when molten or in solution.

3

Find the relation and fill in the blanks:
Catalyst used in Haber process : Fe
Catalyst used in Contact process : ______

Answer: Vanadium pentoxide (V₂O₅)

Explanation: The Contact process for sulfuric acid production uses vanadium pentoxide (V₂O₅) as a catalyst.

4

Match the electron configurations with their valencies:

Answer: (A) X → q, Y → p, Z → s

Explanation:
• X: 2,8,3 → Valency = 3 (q)
• Y: 2,7 → Valency = 7 (p)
• Z: 2,8,2 → Valency = 2 (s)

Questions 5-11 (Each 2 marks) 14 marks total

5

Some compounds and electronegativity values are given: CH₄, K₂O, NH₃
(H = 2.20, C = 2.55, K = 0.82, O = 3.44, N = 3.04)

a) Which is an ionic compound? K₂O
b) Reason: Large electronegativity difference between K (0.82) and O (3.44) > 1.7, indicating ionic character.

6

(A) Information about an atom: Electrons in K, L, M shells; 7 electrons in M shell; 18 neutrons.

a) Electron configuration: 2, 8, 7 (Chlorine)
b) Mass number: 35 (17 protons + 18 neutrons)

OR (B)

Symbols: ¹²C₆, ⁴⁰Ar₁₈, ¹³C₆, ⁴⁰K₁₉, ¹⁵N₇

a) Pair with equal total particles in nucleus: ⁴⁰Ar₁₈ and ⁴⁰K₁₉ (both have mass number 40)
b) Name: Isobars

7

Ammonia is formed when Nitrogen and Hydrogen combine.

a) Balanced equation: N₂ + 3H₂ → 2NH₃
b) Mass of ammonia formed: 34 g (28 g N₂ = 1 mol, 6 g H₂ = 3 mol; N₂ limiting → 2 mol NH₃ = 34 g)

8

(A) Double decomposition reaction: NaCl + AgNO₃ → ?

a) Complete equation: NaCl + AgNO₃ → AgCl↓ + NaNO₃ (A = AgCl, B = NaNO₃)
b) Double decomposition reaction: Reaction where two compounds exchange ions to form two new compounds.

OR (B)

When Ammonium dichromate is heated, Chromium trioxide, water vapour, and Nitrogen are formed.

a) Name: Decomposition reaction
b) Another example: 2HgO → 2Hg + O₂

9

Find oxidation number of manganese in:

a) Mn₂O₇: +7 (2x + 7(-2) = 0 → x = +7)
b) MnO₂: +4 (x + 2(-2) = 0 → x = +4)

10

Transition elements (Groups 3-12)

a) Why called transition elements? They show transition in properties from s-block to p-block elements.
b) Highest energy electrons fill in: d-orbitals of the penultimate (n-1) shell.

11

A solution is prepared by adding 2 g NaCl to 18 g water.

a) Solute: NaCl
b) Mass percentage: 10% (2g/20g × 100)

Questions 12-17 (Each 3 marks) 18 marks total

12

Magnesium oxide is an ionic compound.

a) Electron dot diagram: Mg loses 2 e⁻ to O forming Mg²⁺ and O²⁻
b) Electrons transferred: 2 electrons
c) Anion: Oxide ion (O²⁻)

13

Highly reactive metals react with dilute HCl to produce a gas that burns with a pop sound.

a) Gas: Hydrogen (H₂)
b) More vigorous metal: Magnesium
c) Displacement reaction: A more reactive metal displaces a less reactive metal from its compound.

14

(A) Mg + Cl₂ → MgCl₂

a) Reduced atom: Chlorine (Cl)
b) Reducing agent: Magnesium (Mg)
c) Oxidation reaction: Mg → Mg²⁺ + 2e⁻

OR (B)

H₂ + Cl₂ → 2HCl

a) Oxidation number increased: Hydrogen (0 to +1)
b) Oxidizing agent: Chlorine (Cl₂)
c) Why redox: Both oxidation (H) and reduction (Cl) occur simultaneously.

15

Materials: Sodium thiosulphate, Hydrochloric acid, Boiling tube, Spirit lamp, water

a) Procedure: Add Na₂S₂O₃ and HCl in boiling tube, time cloudiness at different temperatures using spirit lamp to heat.
b) Why rate increases with temperature: Increasing temperature increases kinetic energy of molecules → more collisions → faster reaction rate.

16

Observing reaction of marble pieces and powdered marble with dilute HCl.

a) Influencing factor: Surface area of reactant
b) Gas evolved: Carbon dioxide (CO₂)
c) Chemical equation: CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂

17

(A) Elements X (Group 13) and Y (Group 16) have three shells each.

a) Electron configuration of X: 2,8,3
b) Family of Y: Oxygen family (Chalcogens)
c) Larger atomic size: X (elements on left of periodic table have larger atomic radii)

OR (B)

X is in third period, loses two electrons to attain octet.

a) Electron configuration of X: 2,8,2 (Magnesium)
b) Group: Group 2 (Alkaline earth metals)
c) Noble gas configuration in same period: Argon → 2,8,8

Question 18 (4 marks)

18

(A) Neutralization reactions for preparing calcium phosphate.

a) Acid and alkali: Phosphoric acid (H₃PO₄) and Calcium hydroxide (Ca(OH)₂)
b) Positive ion in alkali: Ca²⁺
c) Chemical formula of salt: Ca₃(PO₄)₂

OR (B)

Hints: Positive ion of alkali is K⁺; Negative ion of acid is SO₄²⁻.

a) Chemical formula of alkali: KOH
b) Chemical formula of acid: H₂SO₄
c) Reaction equation: 2KOH + H₂SO₄ → K₂SO₄ + 2H₂O
d) Name of salt formed: Potassium sulfate

Class 9 Chemistry - Second Term Exam Answer Key

Samagra Shiksha Kerala | Summative Assessment Term II (2025-26)

This is a suggested answer key. Actual evaluation may vary based on examiner's discretion.