Chapter Exam

Chapter-8 Elements — Online MCQ Test

Q: Which of the following is a compound?

Answer: C. Water — Water (H₂O) is a compound made of hydrogen and oxygen elements chemically bonded. The others are elements.

Q: A student burns magnesium in oxygen to form magnesium oxide. Which property is NOT likely to change?

Answer: D. Position in the periodic table — When a compound forms, the constituent elements' position in the periodic table remains fixed; however, their properties (color, melting point, etc.) change significantly.

SCIENCE (CURIOSITY) · CLASS 8th · Karnataka State Board

Practice Chapter-8 Elements with a free chapter-wise online MCQ test for Karnataka State Board CLASS 8th SCIENCE (CURIOSITY). This chapter covers: Compounds. AI-generated questions from basic to board-exam level, with instant results and explanations.

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Chapter-8 Elements — Important Questions & Answers (FAQ)

Frequently asked questions from Karnataka State Board CLASS 8th SCIENCE (CURIOSITY) — Chapter-8 Elements, with answers and explanations. These are sample questions; the exam has its own separate question set.

What is a compound?

A. A pure substance made of two or more elements chemically combined in a fixed ratio ✓
B. A mixture of different elements that are not chemically bonded
C. A single element in pure form
D. A substance that cannot be broken down further

Answer: A. A pure substance made of two or more elements chemically combined in a fixed ratio
A compound is formed when two or more elements combine chemically in fixed proportions with new properties different from the constituent elements.

Which of the following is a compound?

A. Oxygen
B. Iron
C. Water ✓
D. Nitrogen

Answer: C. Water
Water (H₂O) is a compound made of hydrogen and oxygen elements chemically bonded. The others are elements.

What happens to the properties of elements when they form a compound?

A. The properties remain exactly the same
B. The properties combine in a simple average
C. Completely new properties emerge that are different from the constituent elements ✓
D. Only the color changes, other properties remain the same

Answer: C. Completely new properties emerge that are different from the constituent elements
When elements combine to form compounds, they exhibit entirely new properties different from their parent elements, such as hydrogen and oxygen forming water.

A student burns magnesium in oxygen to form magnesium oxide. Which property is NOT likely to change?

A. Color
B. Chemical composition
C. Melting point
D. Position in the periodic table ✓

Answer: D. Position in the periodic table
When a compound forms, the constituent elements' position in the periodic table remains fixed; however, their properties (color, melting point, etc.) change significantly.

In a comprehensive analysis of two substances, scientists find that substance X always contains carbon and hydrogen in a 1:4 atomic ratio, while substance Y contains the same elements in a 1:6 atomic ratio. What is the relationship between X and Y?

A. They are isotopes of the same element
B. They are different compounds with the law of multiple proportions demonstrated ✓
C. They are mixtures of the same elements
D. They cannot both exist in nature

Answer: B. They are different compounds with the law of multiple proportions demonstrated
Different compounds (like CH₄ methane and C₂H₆ ethane) exemplify the law of multiple proportions where the same elements combine in different whole-number ratios, forming distinct compounds.