Master group properties and elements with this SLO-based guide for 9th class. Perfect for Lahore Board and Punjab Boards, aligned with the 2025 syllabus and solved exercises.
Multiple choice Questions
1. Which halogen will have the least reactivity with alkaline earth metals?
- (a) Chlorine
- (b) Bromine
- (c) Iodine
- (d) Fluorine
Correct Answer: (c) Iodine
Explanation: Reactivity decreases as we move down the halogen group because the atomic size increases, making it harder to gain electrons. Iodine is the least reactive among the given options.
Tip: Remember that reactivity of halogens decreases down the group in the periodic table.
2. Which compound do you expect to be colored?
- (a) KCl
- (b) BaCl₂
- (c) AlCl₃
- (d) NiCl₂
Correct Answer: (d) NiCl₂
Explanation: Transition metal compounds like NiCl₂ are often colored due to the d-electrons absorbing specific wavelengths of light.
Tip: If the compound contains a transition metal, it is likely to be colored.
3. In which element exists the strongest forces of attraction between atoms?
- (a) Mg
- (b) Ca
- (c) Sr
- (d) Ba
Correct Answer: (a) Mg
Explanation: Magnesium atoms have a smaller atomic radius and higher charge density compared to the other options, leading to stronger metallic bonding.
Tip: Smaller atomic size and higher charge density usually mean stronger forces of attraction.
4. Elements of which group are all colored?
- (a) Second group
- (b) Sixth group
- (c) Fourth group
- (d) Fifth group
Correct Answer: (b) Sixth group
Explanation: Group 6 elements, particularly transition metals like chromium and molybdenum, form colored compounds.
Tip: Look for transition elements for color trends in compounds.
5. Which halogen acid is unstable at room temperature?
- (a) HBr
- (b) HI
- (c) HCl
- (d) HF
Correct Answer: (b) HI
Explanation: Hydrogen iodide (HI) is unstable because it easily decomposes into hydrogen gas and iodine due to weak bonding between H and I atoms.
Tip: The strength of halogen acids decreases as the size of the halogen atom increases.
6. Which oxide is the most basic?
- (a) Na₂O
- (b) Li₂O
- (c) MgO
- (d) CO
Correct Answer: (a) Na₂O
Explanation: Sodium oxide is a strong basic oxide as it reacts readily with water to form NaOH, a strong base.
Tip: Metal oxides from Group 1 elements are typically the most basic.
7. Which group elements are the most reactive elements?
- (a) Transition metals
- (b) First group
- (c) Second group
- (d) Third group
Correct Answer: (b) First group
Explanation: Group 1 elements (alkali metals) are the most reactive because they have a single electron in their outermost shell, which they lose easily.
Tip: Reactivity increases as you go down Group 1.
8. The following solutions of a halogen and a sodium halide are mixed. Which solution will turn dark because of a reaction?
- (a) Br₂ and NaCl
- (b) Br₂ and NaF
- (c) Cl₂ and NaI
- (d) Cl₂ and NaCl
Correct Answer: (c) Cl₂ and NaI
Explanation: Chlorine is more reactive than iodine, so it displaces iodine from sodium iodide, forming dark iodine (I₂).
Tip: A more reactive halogen can displace a less reactive halogen from its compound.
9. X is a monoatomic gas. Which statement about this is correct?
- (a) X burns in air
- (b) X is colored
- (c) X is unreactive
- (d) X will displace iodine from it
Correct Answer: (c) X is unreactive
Explanation: Monoatomic gases like noble gases are chemically inert due to their stable electronic configuration.
Tip: Noble gases are always monoatomic and unreactive.
10. Which property is correct for Group 1 elements?
- (a) Low electrical conductivity
- (b) High density
- (c) Low melting point
- (d) High melting point
Correct Answer: (c) Low melting point
Explanation: Group 1 metals have relatively low melting points compared to other metals due to their large atomic sizes and weak metallic bonds.
Tip: Group 1 elements exhibit low density, low melting points, and high reactivity.
Short Questions
i. Why does it become easier to cut an alkali metal when we move from top to bottom in Group I?
- Alkali metals become softer as we go down the group because their atoms get larger and the metallic bonds become weaker.
ii. Predict the reactivity of potassium towards halogens.
- Potassium reacts very vigorously with halogens like chlorine to form potassium halides (e.g., KCl), releasing energy and producing a salt.
iii. In the following reaction, chlorine acts as a reducing agent. What is the oxidizing agent?
- The oxidizing agent is NaBr because bromine (Br) is gaining electrons.
iv. Why does iodine exist in the solid state at room temperature?
- Iodine exists as a solid because its molecules are large and have strong intermolecular forces (van der Waals forces) that hold them together in a solid structure.
v. How does Ni catalyze the reaction involving hydrogenation of oil?
- Nickel (Ni) acts as a catalyst by providing a surface where hydrogen and oil molecules can interact more effectively, speeding up the reaction to convert unsaturated fats into saturated fats.
3. Constructed Response Questions
i. Which noble gas should have the lowest boiling point and why?
- Helium has the lowest boiling point because it is the smallest noble gas atom, resulting in the weakest intermolecular forces (London dispersion forces). This makes it easier to convert helium into a gas.
ii. Compare the reactions of alkali metals with chlorine.
- Alkali metals react vigorously with chlorine to form metal chlorides. For example, sodium reacts with chlorine to form sodium chloride (NaCl). The reaction produces heat and light:
2Na+Cl2→2NaCl
iii. Why are almost all the metals solids while non-metals generally exist as gases and solids?
- Metals have strong metallic bonds due to free-moving electrons, which make them solid at room temperature. Non-metals have weak intermolecular forces, which is why many exist as gases or brittle solids.
iv. Name any three elements in the periodic table which exist as liquids.
- Mercury (Hg), Bromine (Br), and Gallium (Ga).
v. Why are transition elements different from normal elements?
- Transition elements have partially filled d-orbitals, which give them unique properties such as variable oxidation states, formation of colored compounds, and catalytic behavior.
vi. Compare the reactivity of chlorine and bromine as reducing agents.
- Chlorine is a stronger oxidizing agent than bromine because it has a higher electronegativity and a smaller atomic size, allowing it to gain electrons more easily.
vii. Which element is the most reactive and which is the least reactive among halogens? Give two reasons to explain your answer.
- Most reactive: Fluorine, because it has the highest electronegativity and smallest atomic size.
Least reactive: Iodine, because it has the lowest electronegativity and largest atomic size among halogens.
4. Descriptive Questions
i. Explain the role of a catalytic converter in an automobile.
- A catalytic converter reduces harmful emissions from vehicle exhaust. It converts toxic gases like carbon monoxide (CO) and nitrogen oxides (NOx) into less harmful gases like carbon dioxide (CO₂) and nitrogen (N₂). Platinum and palladium in the converter act as catalysts.
ii. Why do the chemical reactivities of alkali metals increase down the group, whereas they decrease down the group in case of halogens?
- Alkali metals: Reactivity increases down the group because their atomic size increases, and the outer electron is farther from the nucleus, making it easier to lose.
- Halogens: Reactivity decreases down the group because their atomic size increases, reducing the ability to gain electrons due to weaker nuclear attraction.
iii. Why are metals generally tough and strong, whereas non-metals are neither tough nor strong?
- Metals: They have strong metallic bonds formed by a “sea” of free electrons that hold the metal ions together, making them tough and strong.
- Non-metals: They have weak covalent bonds or intermolecular forces, making them brittle or soft.
iv. Both alkali metals and halogens are very reactive elements with roles opposite to each other. Explain.
- Alkali metals lose electrons to form positive ions (cations), making them strong reducing agents. Halogens gain electrons to form negative ions (anions), making them strong oxidizing agents. Their reactivity arises due to their tendency to achieve stable electronic configurations.
v. Why is hydrogen bromide thermally unstable compared to hydrogen chloride?
- Hydrogen bromide has a weaker bond compared to hydrogen chloride because bromine is larger than chlorine, resulting in a longer and weaker bond. This makes HBr decompose at lower temperatures.
vi. Compare the properties of metals and non-metals.
- Metals: Good conductors of heat and electricity, malleable, ductile, and have high melting points.
- Non-metals: Poor conductors of heat and electricity, brittle, not ductile, and generally have lower melting points.
vii. Why is V₂O₅ catalyst preferred over platinum in the oxidation of sulfur dioxide? Give reasons.
- V₂O₅ is less expensive, more efficient at high temperatures, and remains stable during the oxidation process, whereas platinum is costly and can be poisoned by impurities.
5. Investigative Questions
i. Explain the role of sodium as a heat transfer agent in the atomic nuclear power plant. Which property of sodium is utilized in this role?
- Sodium is used because it has a high thermal conductivity and a wide liquid temperature range. It efficiently transfers heat from the reactor to the steam generator without boiling at high temperatures.
ii. Why and how does lithium behave differently from the rest of the alkali metals?
- Lithium has a smaller atomic size, higher ionization energy, and stronger covalent character. It reacts less vigorously with water and forms a stable oxide (Li₂O) instead of a peroxide or superoxide.
iii. Why aluminum metal is used in the manufacture of cooking utensils, whereas magnesium is not considered useful for this purpose?
- Aluminum is lightweight, has good thermal conductivity, and resists corrosion due to the formation of an oxide layer. Magnesium, though lightweight, is not preferred because it is less durable and reacts more readily with food and water.
