General Science — Past Papers — Part 6 MCQs with Explanations

A chemical reaction that releases heat energy to the surroundings is called an Exothermic Reaction . In such reactions, energy is produced in the form of heat, light, or flames . Examples include combustion of fuel, respiration, and neutralization reactions . Additional information : An endothermic reaction , which absorbs heat from the surroundings.

The branch of chemistry that studies heat energy released or absorbed during chemical reactions is called Thermochemistry . It explains how heat changes occur during reactions such as combustion, neutralization, and dissolution . It deals with concepts like enthalpy change (ΔH), exothermic reactions, and endothermic reactions.

The formation of hydrogen and oxygen from water , which is an example of a decomposition reaction: 2H2O → 2H2 + O2 In this reaction , water (H2O) decomposes into hydrogen (H2) and oxygen (O2).

A Telescope is an optical instrument used to observe distant objects such as stars, planets, and galaxies . It collects and magnifies light or other forms of electromagnetic radiation . The term “ telescope ” was coined in 1611 by the Greek mathematician Giovanni Demisiani .

When water cools from 4°C to 0°C , it expands as it freezes into ice. Unlike most substances, water’s maximum density is at 4°C ; below this temperature, the volume increases and density decreases . This is why ice floats on water.

Combustion is a chemical reaction in which a substance reacts rapidly with oxygen to produce heat and light . Commonly observed when wood, coal, or fuel burns . Combustion is an exothermic reaction because it releases energy.

Antoine Lavoisier , a French chemist , is credited with discovering the law of conservation of mass in 1789 (1785) . He demonstrated that matter cannot be created or destroyed in a chemical reaction, only transformed from one substance to another.

Chlorofluorocarbons (CFCs) are chemical compounds used in refrigerators, air conditioners, and aerosol sprays . When released into the atmosphere, CFCs destroy the ozone layer by breaking down O₃ molecules. The ozone layer protects Earth from harmful ultraviolet (UV) radiation.

Mitosis is the process by which a single cell divides to produce two identical daughter cells . It is essential for growth, tissue repair, and development in multicellular organisms. Mitosis maintains the same number of chromosomes in each new cell. Additional information : Meiosis is different; it occurs in sex cells and reduces chromosome number by half.

The stomach is an organ involved in digestion , not waste elimination. The four parts of body play important role in eliminating waste material from our body Lungs : remove carbon dioxide through exhalation Kidneys : filter waste and excess substances from the blood, producing urine Skin : removes waste through sweating Liver : detoxifies harmful substances and aids in their removal

Car brakes are typically hydraulic systems , not pneumatic systems. The examples of pneumatic systems : Spray gun : uses compressed air to atomize and spray paint or other materials. Bicycle pump : uses compressed air to inflate tires. Vacuum cleaner : uses compressed air to create suction and lift dust and debris.

Pascal's Law states that the pressure applied to a fluid (liquid or gas) in a container is transmitted equally throughout the fluid and to the walls of the container , and that the pressure is the same in all directions at a given point in the fluid. This principle has numerous applications in engineering, physics, and everyday life.

Reflex actions are rapid, automatic responses to stimuli that occur without the involvement of the brain. Instead, they are mediated by the spinal cord or peripheral nerves.

The structure of the brain is similar to the structure of a Walnut , with both having: A hard outer layer ( cranium vs. shell ) A wrinkled surface ( brain's cerebral cortex vs. walnut's surface ) A distinct left and right half ( brain's hemispheres vs. walnut's halves )

The nervous system is the body system that controls and coordinates the functions of all other organ systems. It allowing for integration and regulation of various bodily functions. It consists of the brain, spinal cord, nerves, and sensory organs.

The incorrect statement is : States of matter does not change during chemical reactions. During chemical reactions , states of matter can change. For example , a solid may dissolve in a liquid , a liquid may vaporize, or a gas may condense into a liquid.

The ozone layer acts as Earth’s natural sunscreen, protecting life from the sun’s harmful ultraviolet (UV) radiation . UV radiation can cause skin cancer, eye damage, and harm to plants and animals . Additional information : Chemical Formula: O₃ (three oxygen atoms) Layer Location: Stratosphere, 15–40 km above Earth Function: Absorbs UV-B and UV-C rays from the Sun Depletion Causes: Air pollution, CFCs, industrial chemicals Protection Measures: Reduce CFC use, ozone-friendly products

Melting of ice is a physical change , as it only involves a change in state (from solid to liquid) without a change in chemical composition. The examples of chemical changes: Burning of fuel Explosion of firework Burning of wood Cooking of food (breakfast, lunch, dinner) Bursting of crackers Burning of wax Rusting of iron Heating sulphur with iron fillings (to produce iron sulphide) Digestion of food Respiration in living things Photosynthesis in plants

In a concave mirror, the image size depends upon the : Position of the object relative to the mirror's focal point (f ) Center of curvature( C) Additional information Concave lenses are also known as diverging lenses. Last updated on 09-03-2026

Definition: Possess both magnitude and direction. Representation : Represented by arrows, where the length indicates magnitude and the arrowhead indicates direction. Examples: Displacement Velocity Acceleration Force Momentum Additional information Difference from Scalars: Unlike scalars, which only have magnitude (e.g., speed), vectors require both to be fully defined Last updated on 09-03-2026

Weight is a vector quantity Because it is a force defined as the product of mass and the acceleration due to gravity ( W = mg). It has both magnitude (amount of force) and direction (downward, towards the center of the Earth) Additional information Mass, Time, and temperature are scalar quantities Last updated on 09-03-2026

A solution is a homogeneous mixture of a solute dissolved in a solvent. It consists of a solute (dissolved substance) and a solvent (dissolving medium). The solute is evenly distributed , creating a uniform composition. Examples : Sugar in water, salt in water, gasoline. Question updated on 08 march 2026

An inclined plane is a flat surface tilted at an angle to help move objects up or down with less effort. It reduces the force needed compared to lifting vertically. Mechanical advantage = distance along incline ÷ vertical height .

Iodine deficiency can cause mental retardation in children . Particularly if the deficiency occurs during fetal development or early childhood. This is because iodine is essential for brain development and thyroid function.

Peanuts are a legume and a good source of protein, It containing about 20.5 grams of protein per 100 grams . Additional information : Apples : 0.3 grams of protein per medium-sized fruit Watermelon : 0.6 grams of protein per cup Mango : 1.4 grams of protein per cup

Weight depends on gravitational force acting on mass. The Moon’s gravity is about 1/6th of Earth’s , so your weight decreases. Your mass remains the same , only weight changes. Additional information : Weight change occurs due to difference in gravity. Mass is constant everywhere in the universe.

Weight is the force of gravity acting on an object's mass. It depends on mass of the object and gravitational acceleration (g). Formula: Weight (W) = Mass × Gravity (W = m × g) Additional information : Earth : g ≈ 9.8 m/s² Moon : g ≈ 1.6 m/s² (weight is less)

Frictional force arises when two surfaces slide or move against each other. It opposes the motion and can generate heat . Friction is essential in walking, driving, and machine operation.

A diluted solution has a low ratio of solute to solvent, meaning it contains less solute. It is the opposite of a concentrated solution , which has more solute. Diluted solutions are often used when a weaker solution is needed.

Paper Chromatography is a method used to separate and identify colored substances, especially dyes in a mixture. It works based on different rates of movement of substances through absorbent paper with a solvent. Additional information : Filtration – separates solids from liquids. Sublimation – separates a solid that sublimes from a mixture. Distillation – separates liquids based on boiling points.

A molecule is the smallest particle of a compound that retains the chemical properties of that compound. It is made up of two or more atoms chemically bonded together. Molecules can be elements ( O₂, N₂ ) or compounds ( H₂O, CO₂ ).

The correct answer is: Molecules do not collide with one another Gas molecules: Are widely separated Have low attractive forces Are free to move in any direction Collide with one another

Magnetic field lines form a closed loop around a magnet. Outside the bar magnet, they go from the north pole to south pole . Inside the bar magnet, they return from south pole to north pole . This continuous path shows the c omplete magnetic field cycle . Therefore, inside a bar magnet th e direction is south → north . Question updated on 08 march 2026

Carnivores are animals that eat only meat , primarily from other animals. Examples of carnivores include lions, tigers, bears, wolves, and sharks. Additional information: Animals that eat plants exclusively are herbivores . Animals that eat both plants and meat are called omnivores .

Decomposers are organisms that break down dead and waste products, releasing useful elements such as carbon, nitrogen, and phosphorus back into the soil and environment. This process is called decomposition, and it's an essential step in the nutrient cycle. Decomposers include organisms like : Bacteria Fungi (such as mushrooms) Detritivores (such as earthworms and insects) By breaking down organic matter, decomposers help to : Recycle nutrients Improve soil structure and fertility Support plant growth and development

Amphibians are animals that live both in water and on land . Most amphibians lay their eggs in water because their eggs do not have a protective shell. Examples of Amphibians: Frog, Toad, Salamander, Newt, Caecilian

A parachute increases air resistance (drag) when it opens in the air. This slows down the falling speed of a skydiver , allowing a safe landing. Forces acting on a skydiver: Gravity (pulls downward) Air resistance (pushes upward)

An iron nail/steel rod can be magnetized by passing an electric current around it , a process known as electromagnetic induction. This is the principle behind electromagnets.

Friction is a force that opposes motion between two surfaces in contact. It slows down or stops objects when they move against each other. Friction helps us walk, write, and hold objects without slipping. Too much friction can cause heat and wear in machines.

An eraser is usually made of rubber , which does not attract magnets. Magnetic materials are substances that are attracted by a magnet. Materials like iron and steel are magnetic, while rubber or plastic items are non-magnetic. Additional information : Common Magnetic Materials : Iron Nickel Cobalt Steel (paper clip, iron nail) Some alloys Non-magnetic examples : Rubber, wood, plastic, paper.