These essential MCQ questions are selected from the most important topics in ICSE Class 9 Science 2026 as per the latest CISCE syllabus. Sections include Matter & its Composition, Force & Motion, Heat & Energy, Light, Cell Structure, Plant Physiology, and the Periodic Table. For truly unlimited daily MCQ practice, visit Vooo AI Education.
🔭 ICSE Class 9 Science
1According to Dalton's atomic theory, atoms of the same element are:
Answer: B — Identical in all properties
Dalton's atomic theory (1808) states: all matter is made of indivisible atoms; atoms of the same element are identical in mass and properties; atoms of different elements differ in mass and properties; atoms combine in simple whole number ratios to form compounds; atoms cannot be created or destroyed. Later discoveries (isotopes, subatomic particles) modified some postulates, but the theory was the foundation of modern chemistry.
Dalton's atomic theory (1808) states: all matter is made of indivisible atoms; atoms of the same element are identical in mass and properties; atoms of different elements differ in mass and properties; atoms combine in simple whole number ratios to form compounds; atoms cannot be created or destroyed. Later discoveries (isotopes, subatomic particles) modified some postulates, but the theory was the foundation of modern chemistry.
2The SI unit of force is:
Answer: C — Newton
The SI unit of force is the Newton (N), named after Sir Isaac Newton. 1 Newton = 1 kg·m/s² (the force required to accelerate a 1 kg mass at 1 m/s²). From Newton's second law: F = ma. Joule (J) is the unit of energy/work. Watt (W) is the unit of power. Pascal (Pa) is the unit of pressure. 1 Pa = 1 N/m². Force is a vector quantity — it has both magnitude and direction.
The SI unit of force is the Newton (N), named after Sir Isaac Newton. 1 Newton = 1 kg·m/s² (the force required to accelerate a 1 kg mass at 1 m/s²). From Newton's second law: F = ma. Joule (J) is the unit of energy/work. Watt (W) is the unit of power. Pascal (Pa) is the unit of pressure. 1 Pa = 1 N/m². Force is a vector quantity — it has both magnitude and direction.
3Heat always flows from a body at:
Answer: B — Higher temperature to lower temperature
Heat naturally flows from a hotter body (higher temperature) to a colder body (lower temperature) — this is the Second Law of Thermodynamics. Heat flow stops when both bodies reach the same temperature (thermal equilibrium). Methods of heat transfer: conduction (solids — particle vibration), convection (fluids — particle movement), and radiation (no medium needed — electromagnetic waves). Sun heats Earth by radiation through the vacuum of space.
Heat naturally flows from a hotter body (higher temperature) to a colder body (lower temperature) — this is the Second Law of Thermodynamics. Heat flow stops when both bodies reach the same temperature (thermal equilibrium). Methods of heat transfer: conduction (solids — particle vibration), convection (fluids — particle movement), and radiation (no medium needed — electromagnetic waves). Sun heats Earth by radiation through the vacuum of space.
4Which of the following undergoes total internal reflection?
Answer: A — Light going from glass to air at angle greater than critical angle
Total internal reflection occurs when light travels from a denser medium (glass, water) to a rarer medium (air) at an angle of incidence greater than the critical angle. All light is reflected back into the denser medium — no refraction occurs. Applications: optical fibres (internet, medical endoscopes), diamonds (sparkle), mirages, and periscopes. Critical angle for glass-air = about 42°; for water-air = about 49°.
Total internal reflection occurs when light travels from a denser medium (glass, water) to a rarer medium (air) at an angle of incidence greater than the critical angle. All light is reflected back into the denser medium — no refraction occurs. Applications: optical fibres (internet, medical endoscopes), diamonds (sparkle), mirages, and periscopes. Critical angle for glass-air = about 42°; for water-air = about 49°.
5The process by which plants absorb water from soil through roots is called:
Answer: C — Osmosis
Water absorption by roots occurs mainly through osmosis — the movement of water from a region of higher water concentration (dilute soil solution) to lower water concentration (root hair cells) through a semi-permeable membrane. Root hair cells have a higher solute concentration than soil water. Transpiration is the loss of water vapour through stomata. Diffusion is movement of particles from high to low concentration (no membrane required).
Water absorption by roots occurs mainly through osmosis — the movement of water from a region of higher water concentration (dilute soil solution) to lower water concentration (root hair cells) through a semi-permeable membrane. Root hair cells have a higher solute concentration than soil water. Transpiration is the loss of water vapour through stomata. Diffusion is movement of particles from high to low concentration (no membrane required).
6In the Modern Periodic Table, elements are arranged in order of their:
Answer: B — Atomic number
In the Modern Periodic Table (Moseley's, 1913), elements are arranged in increasing order of atomic number (number of protons). Mendeleev arranged elements by atomic mass (1869) but this created anomalies (e.g., Argon and Potassium). The Modern Table has 18 groups (vertical columns) and 7 periods (horizontal rows). Elements in the same group have the same number of valence electrons and similar chemical properties.
In the Modern Periodic Table (Moseley's, 1913), elements are arranged in increasing order of atomic number (number of protons). Mendeleev arranged elements by atomic mass (1869) but this created anomalies (e.g., Argon and Potassium). The Modern Table has 18 groups (vertical columns) and 7 periods (horizontal rows). Elements in the same group have the same number of valence electrons and similar chemical properties.
7The work done when a force of 10 N moves an object 5 m in the direction of force is:
Answer: C — 50 J
Work = Force × Distance × cosθ. When force and displacement are in the same direction, θ = 0° and cos0° = 1. W = 10 N × 5 m × 1 = 50 J (Joules). Work is a scalar quantity. Work done is zero when force is perpendicular to displacement (e.g., a person carrying a bag walking horizontally). Negative work is done when force is opposite to displacement (e.g., friction). 1 Joule = 1 Newton × 1 metre.
Work = Force × Distance × cosθ. When force and displacement are in the same direction, θ = 0° and cos0° = 1. W = 10 N × 5 m × 1 = 50 J (Joules). Work is a scalar quantity. Work done is zero when force is perpendicular to displacement (e.g., a person carrying a bag walking horizontally). Negative work is done when force is opposite to displacement (e.g., friction). 1 Joule = 1 Newton × 1 metre.
8Which part of the cell is called the fluid mosaic model?
Answer: B — Cell membrane
The fluid mosaic model (Singer and Nicolson, 1972) describes the structure of the cell membrane (plasma membrane). It consists of a phospholipid bilayer (fluid) in which proteins are embedded (mosaic). The membrane is selectively permeable — it controls what enters and exits the cell. The cell wall (in plants, fungi, bacteria) is rigid and made of cellulose (plants) or chitin (fungi). The cell membrane is present in all cells.
The fluid mosaic model (Singer and Nicolson, 1972) describes the structure of the cell membrane (plasma membrane). It consists of a phospholipid bilayer (fluid) in which proteins are embedded (mosaic). The membrane is selectively permeable — it controls what enters and exits the cell. The cell wall (in plants, fungi, bacteria) is rigid and made of cellulose (plants) or chitin (fungi). The cell membrane is present in all cells.
9The number of valence electrons in a chlorine atom (atomic number 17) is:
Answer: C — 7
Chlorine has atomic number 17. Electronic configuration: 2, 8, 7 (K=2, L=8, M=7). Valence electrons are in the outermost shell = 7. Chlorine needs 1 more electron to complete its octet (8 electrons in outermost shell), so it has valency of 1. It belongs to Group 17 (halogens) in the Modern Periodic Table. Halogens are highly reactive non-metals. Valence electrons determine the chemical behaviour of an element.
Chlorine has atomic number 17. Electronic configuration: 2, 8, 7 (K=2, L=8, M=7). Valence electrons are in the outermost shell = 7. Chlorine needs 1 more electron to complete its octet (8 electrons in outermost shell), so it has valency of 1. It belongs to Group 17 (halogens) in the Modern Periodic Table. Halogens are highly reactive non-metals. Valence electrons determine the chemical behaviour of an element.
10Stomata in plants are mainly responsible for:
Answer: C — Gaseous exchange and transpiration
Stomata are tiny pores on leaf surfaces (mostly on lower epidermis) surrounded by guard cells. Their primary functions are: (1) gas exchange — CO₂ enters for photosynthesis, O₂ exits; O₂ enters for respiration, CO₂ exits; (2) transpiration — loss of water vapour. Guard cells control opening/closing of stomata by changing their turgor pressure. Stomata open in light and close in dark. Transpiration creates a suction pull that draws water up through xylem.
Stomata are tiny pores on leaf surfaces (mostly on lower epidermis) surrounded by guard cells. Their primary functions are: (1) gas exchange — CO₂ enters for photosynthesis, O₂ exits; O₂ enters for respiration, CO₂ exits; (2) transpiration — loss of water vapour. Guard cells control opening/closing of stomata by changing their turgor pressure. Stomata open in light and close in dark. Transpiration creates a suction pull that draws water up through xylem.
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