Questions on Elements and Compounds
Multiple-Choice Questions – Elements and Compounds
1. What is an element?
A) A combination of two or more atoms
B) A substance made of different molecules
C) A substance that cannot be broken down chemically into simpler substances
D) A mixture of atoms
E) A synthetic material
2. Which of the following is a compound?
A) Gold
B) Water
C) Oxygen
D) Nitrogen
E) Carbon
3. Which is an example of an element?
A) Salt
B) Water
C) Sugar
D) Iron
E) Carbon dioxide
4. What distinguishes an element from a compound?
A) Elements are pure; compounds are mixtures
B) Elements can be separated by filtration
C) Compounds consist of two or more elements chemically bonded
D) Elements are heavier than compounds
E) Compounds are found only in nature
5. Which of these is a compound?
A) H₂
B) Na
C) O₂
D) H₂O
E) C
6. Which of the following is not an element?
A) Neon
B) Silver
C) Air
D) Hydrogen
E) Helium
7. Which particle represents the smallest unit of an element?
A) Cell
B) Electron
C) Atom
D) Ion
E) Molecule
8. Which of the following is a diatomic element?
A) He
B) Ne
C) N₂
D) Fe
E) Al
9. Which of the following best describes a compound?
A) A mixture of molecules
B) A substance made of identical atoms
C) A substance composed of atoms of different elements in a fixed ratio
D) A non-pure substance
E) An ionically bonded metal
10. Which of the following is a molecular compound?
A) NaCl
B) CO₂
C) Fe
D) O₂
E) Al
11. Which of the following contains only one kind of atom?
A) CO
B) NO₂
C) O₃
D) H₂O
E) NaCl
12. What is true about compounds?
A) Their components retain their individual properties
B) They are made by physical combinations
C) They have fixed chemical formulas
D) They can be separated by filtration
E) They are always metallic
13. A compound always has:
A) Only one element
B) More than one molecule
C) A definite composition
D) Variable chemical formulas
E) No atoms
14. Which of the following is a compound used by living organisms?
A) H₂
B) O₂
C) CO₂
D) Fe
E) Ag
15. Which of the following is an element and a gas at room temperature?
A) Chlorine
B) Iron
C) Mercury
D) Sodium
E) Calcium
16. How are elements represented in chemical formulas?
A) By numbers
B) By pictures
C) By symbols
D) By their mass
E) By compounds
17. Which is a correct example of a compound formula?
A) O
B) CO
C) Na
D) H
E) Fe
18. A compound is a substance that:
A) Is found only in living things
B) Contains only one kind of atom
C) Can be separated by physical means
D) Has atoms of two or more elements
E) Is always liquid
19. Which of the following is a metallic element?
A) Oxygen
B) Sodium
C) Chlorine
D) Nitrogen
E) Helium
20. Water is classified as a:
A) Homogeneous element
B) Heterogeneous mixture
C) Compound
D) Pure element
E) Gas
21. Which of the following is not a compound?
A) Ammonia
B) Carbon dioxide
C) Hydrogen
D) Table salt
E) Water
22. Elements in the periodic table are arranged by:
A) Melting point
B) Atomic number
C) Color
D) Mass
E) Physical state
23. Which of the following is made of two nonmetal elements?
A) CO₂
B) NaCl
C) Fe₂O₃
D) CaCl₂
E) AgNO₃
24. Which element is essential for breathing?
A) Helium
B) Nitrogen
C) Hydrogen
D) Oxygen
E) Argon
25. A molecule of water contains:
A) Two hydrogen atoms only
B) Two oxygen atoms only
C) Two hydrogen and one oxygen atom
D) One hydrogen and two oxygen atoms
E) Three hydrogen atoms
26. Which statement about elements is correct?
A) They are always gases
B) They can be broken into simpler substances
C) They are pure substances made of only one kind of atom
D) They always contain metals
E) They are unstable
27. A chemical formula shows:
A) The mass of the elements
B) The type and number of atoms in a compound
C) The color of the substance
D) The boiling point
E) The density
28. Which of these is a compound that exists naturally?
A) NaCl
B) Br
C) Al
D) H
E) C
29. Which of the following is a pure substance?
A) Air
B) Sugar water
C) Carbon monoxide
D) Soda
E) Milk
30. Which term refers to a substance made up of two or more elements chemically combined?
A) Mixture
B) Colloid
C) Element
D) Solution
E) Compound
- Questions on Physical Change
- Questions on Mixtures, Homogeneous and Heterogeneous Mixtures
- Questions on Separating Mixtures
Answer Key with Explanations
1. C) An element cannot be chemically broken into simpler substances.
2. B) Water (H₂O) is a compound of hydrogen and oxygen.
3. D) Iron (Fe) is an element.
4. C) Compounds consist of chemically bonded atoms of different elements.
5. D) H₂O is a compound; the others are elements.
6. C) Air is a mixture, not a single element.
7. C) The atom is the smallest unit of an element.
8. C) N₂ (nitrogen gas) is a diatomic element.
9. C) Compounds have atoms of different elements in fixed ratios.
10. B) CO₂ is a molecular compound of carbon and oxygen.
11. C) O₃ (ozone) has only oxygen atoms.
12. C) Compounds have fixed formulas and defined properties.
13. C) Compounds have definite, unchanging compositions.
14. C) CO₂ is used in respiration and photosynthesis.
15. A) Chlorine is a gaseous element at room temperature.
16. C) Elements are represented by chemical symbols (e.g., O, Fe).
17. B) CO (carbon monoxide) is a compound.
18. D) Compounds consist of atoms of two or more different elements.
19. B) Sodium is a metallic element.
20. C) Water is a compound (H₂O).
21. C) Hydrogen is an element, not a compound.
22. B) Elements are arranged by increasing atomic number.
23. A) CO₂ has carbon and oxygen—both nonmetals.
24. D) Oxygen is required for cellular respiration.
25. C) Water = 2 hydrogen + 1 oxygen atom.
26. C) Elements are pure substances with identical atoms.
27. B) A chemical formula shows atom types and counts.
28. A) NaCl (salt) is a naturally occurring compound.
29. C) Carbon monoxide is a pure compound.
30. E) A compound is a chemical combination of elements.
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