15 extra multiple-choice questions for Periodic Classification of Elements (10th Standard Science, Samacheer Kalvi), beyond the ones printed in the textbook — each with the correct option highlighted and a clear, worked explanation. Free to read in English and Tamil.
Q1
Which of the following periods is the shortest period in the modern periodic table, containing only two elements?
- A. First periodCorrect
- B. Second period
- C. Third period
- D. Seventh period
Explanation. The first period is the shortest period in the modern periodic table. It contains only two elements, which are hydrogen and helium.
Q2
During Baeyer's process for the purification of bauxite, what soluble compound is formed when bauxite is heated with concentrated caustic soda?
- A. Sodium meta-aluminateCorrect
- B. Aluminium hydroxide
- C. Sodium silicate
- D. Aluminium silicate
Explanation. In Baeyer's process, finely powdered bauxite ore is heated with concentrated caustic soda (NaOH) solution under pressure to form soluble sodium meta-aluminate, leaving insoluble impurities behind.
Q3
What is the primary purpose of adding fluorspar (\(CaF_2\)) along with cryolite and alumina in the electrolytic reduction of alumina?
- A. To act as a catalyst for faster deposition
- B. To lower the fusion temperature of the electrolyte mixtureCorrect
- C. To increase the electrical conductivity of the cathode lining
- D. To prevent the oxidation of the carbon anodes
Explanation. Fluorspar is added to alumina and molten cryolite in Hall's process to lower the fusion temperature of the electrolyte mixture, which helps conserve energy during extraction.
Q4
In the metallurgy of iron, roasted iron ore, coke, and limestone are mixed and fed into the blast furnace. What is the correct ratio of these components in the charge?
- A. 1:4:8
- B. 4:8:1
- C. 8:4:1Correct
- D. 8:1:4
Explanation. The charge used in the metallurgy of iron consists of roasted iron ore, coke, and limestone in the weight ratio of 8:4:1. This is fed into the blast furnace from the top.
Q5
Aluminium metal is not attacked by concentrated nitric acid (\(HNO_3\)). What is the reason for this passivity?
- A. Nitric acid is a weak acid and cannot react with active metals
- B. Formation of a protective passive oxide film on the metal surfaceCorrect
- C. Aluminium has a very high positive electronegativity value
- D. The reaction is highly endothermic and requires high temperatures
Explanation. Concentrated nitric acid does not attack aluminium because it renders the metal passive by forming a thin protective layer of aluminium oxide on its surface.
Q6
On exposure to moist air, copper vessels form a green layer on their surface. What is the chemical composition of this green layer?
- A. Copper oxide
- B. Basic copper carbonateCorrect
- C. Copper sulphate
- D. Hydrated copper chloride
Explanation. When copper is exposed to moist air containing carbon dioxide and oxygen, it undergoes corrosion to form a green layer of basic copper carbonate on its surface.
Q7
Which form of iron has the lowest carbon content, making it the purest commercial variety of iron?
- A. Pig iron
- B. Cast iron
- C. Steel
- D. Wrought ironCorrect
Explanation. Wrought iron is the purest commercial variety of iron, containing less than 0.25% carbon, which is lower than the carbon content of steel and cast iron.
Q8
Which of the following is the chief ore of copper, yielding about 76% of the world's copper production?
- A. Cuprite
- B. Copper glanz
- C. Copper pyritesCorrect
- D. Azurite
Explanation. Copper pyrites (\(CuFeS_2\)) is the chief ore of copper. It is the main mineral source from which about 76% of the world's copper is extracted.
Q9
Dental amalgam, used for filling tooth cavities, is an alloy of mercury with which other metals?
- A. Aluminium and copper
- B. Silver and tinCorrect
- C. Gold and platinum
- D. Lead and zinc
Explanation. Silver-tin (Ag-Sn) amalgam is an alloy of mercury with silver and tin, commonly used in dentistry for filling tooth cavities.
Q10
In Mendeleev's periodic table, which element with a higher atomic mass of 39.95 amu was placed before potassium (atomic mass 39.10 amu) to group it with elements of similar properties?
- A. Helium
- B. Neon
- C. ArgonCorrect
- D. Krypton
Explanation. Argon (atomic mass 39.95 amu) was placed before potassium (atomic mass 39.10 amu) in the periodic table because argon is an inert gas and belongs with other noble gases.
Q11
Which of the following periodic properties increases as you move from top to bottom down a group in the periodic table?
- A. Ionisation energy
- B. Electron affinity
- C. Electronegativity
- D. Atomic radiusCorrect
Explanation. Atomic radius increases down a group because new electronic shells are added, while ionisation energy, electron affinity, and electronegativity decrease down a group.
Q12
What is the scientific term used for the rocky, earthy, or sandy impurities associated with an ore in its natural state?
- A. Slag
- B. Flux
- C. GangueCorrect
- D. Matte
Explanation. Gangue (or matrix) is the term used for the unwanted rocky, earthy, or siliceous impurities associated with an ore.
Q13
Which group of elements in the modern periodic table is known as the family of noble gases?
- A. Group 15
- B. Group 16
- C. Group 17
- D. Group 18Correct
Explanation. Group 18 contains noble gases such as helium, neon, argon, krypton, xenon, and radon, which have stable electronic configurations.
Q14
What term is used to describe the entire scientific and technological process of extracting a metal from its ore and refining it?
- A. Bessemerisation
- B. Smelting
- C. MetallurgyCorrect
- D. Calcination
Explanation. Metallurgy is the science and technology of extracting metals from their ores and preparing them for practical use.
Q15
How many elements are present in the fourth period of the modern periodic table, starting from potassium and ending with krypton?
- A. 8 elements
- B. 18 elementsCorrect
- C. 32 elements
- D. 2 elements
Explanation. The fourth period is a long period that contains 18 elements, which includes 8 normal elements and 10 transition elements, starting from potassium and ending with krypton.
