General Science — Past Papers — Part 3 MCQs with Explanations

Sirius means صبح کا ستارہ Sirius , also called the Dog Star . It is the brightest star in the night sky visible without a telescope. It is located in the constellation Canis Major . It is about 8.6 light-years from Earth.

Earth is located in the Milky Way Galaxy . It a spiral galaxy containing hundreds of billions of stars . Our Solar System is one of the many systems within this galaxy.

Copper is an excellent conductor of heat . It having a high thermal conductivity (386 W/mK). This means it can efficiently transfer heat energy with minimal resistance. Metals (e.g., iron, copper, silver, mercury, aluminum ) are good conductors of heat.

In liquids and gases , heat is mainly transferred by convection . Convection involves the movement of particles carrying heat from one place to another . Essential for weather patterns, ocean currents , and heating systems.

Noise intensity is measured in decibels (dB). It indicates the loudness of sound . It helps assess noise pollution in cities, industries, and traffic areas . Noise pollution affects hearing, stress levels, and sleep . Reducing exposure above 85 dB is important for health protection .

The flash of light from lightning is a form of electromagnetic radiation , and as such, it travels at the speed of light. It is denoted by the letter c . It is equal to: 3 x 10^8 meters per second (m/s) in scientific notation. 300,000 kilometers per second (km/s) in metric units. 186,282 miles per second (mi/s) in imperial units

Tritium , also known as superheavy hydrogen . It has 1 proton and 2 neutrons in its atomic nucleus. Additional information : Protium (¹H) → 1 proton, 0 neutrons Deuterium (²H) → 1 proton, 1 neutron

The K orbit , also known as the first electron shell. It can hold a maximum of 2 electrons. The L orbit, also known as the second electron shell. It can hold a maximum of 8 electrons. The M orbit, also known as the third electron shell. It can hold a maximum of 18 electrons.

The mass number (A) is the sum of protons and neutrons present in the nucleus of an atom. It is a measure of the total number of nucleons (protons and neutrons) in the nucleus. It helps determine the atomic mass and distinguishes isotopes of an element.

Halazone tablets are used to purify drinking water by killing bacteria and pathogens . Commonly used in emergencies, military, or travel situations where safe water is unavailable. Halazone tablets can purify 1 liter of water in about 5–10 minutes .

About 97.5% of the water on Earth is saltwater , found in oceans, seas, and salt lakes. The remaining 2.5% is freshwater , found in rivers, lakes, wetlands , and underground aquifers.

Cat and Dog is/are a secondary consumer . Because they eats primary consumers (herbivores). Like mice, birds, and rabbits .

The olfactory bulb is a structure in the brain responsible for processing smells detected by the nose . It receives signals from olfactory receptor neurons and sends them to other brain regions for interpretation. Location: underside of the frontal lobe of the brain

The ear canal ( external auditory canal ) transmits sound waves from the outer ear to the eardrum in the middle ear. It acts as a conduit, amplifying sound slightly and protecting the inner structures. Ear Canal length: ~ 2.5 cm in adults

The iris is the colored part of the eye (blue, brown, green, etc.). It controls the size of the pupil, regulating how much light enters the eye. Additional information : Pupil – black opening for light Cornea – transparent front layer Lens – focuses light Retina – receives image

Comets : huge masses of snow and rocks that revolve around the Sun in orbits. Comets : have huge glowing tails. Halley's Comet was last seen in: 1986 Halley's Comet will be next seen in : 2062

Apollo 11 was the mission that successfully landed astronauts . Neil Armstrong and Buzz Aldrin on the moon on July 20, 1969 .

If an object absorbs all seven colors of light (i.e., all the wavelengths of visible light), it appears black . This is because no light is being reflected , and our eyes perceive the absence of light as black. When an object reflects all the component colors of light, it appears white .

Security mirrors are typically convex mirrors. The examples of concave mirrors: Cosmetic mirrors (makeup mirrors) Dentist mirrors Car headlight mirrors

A kaleidoscope is an optical instrument that creates symmetrical, colorful multiple images using mirrors and colored objects. When rotated, it continuously forms new patterns of images . Commonly used for educational purposes and toys .

Reflection occurs when light bounces back from a surface instead of passing through it. Shiny or smooth surfaces like mirrors produce clear and regular reflections. This principle is used in mirrors, periscopes, and optical instruments .

Kinetic energy is the energy an object possesses due to its motion. Any moving object, such as a car, a ball, or a person , has kinetic energy. The amount of kinetic energy an object has depends on its mass and velocity .

A saturated solution contains the maximum amount of solute that can dissolve at a given temperature. Any additional solute added will remain undissolved. Example: Sugar in water at room temperature reaches saturation when no more sugar dissolves. If a solution contains less solute than the maximum, it is called unsaturated .

Nitrogen (N₂) makes up about 78% of Earth's atmosphere . It is a colorless, odorless, and inert gas, essential for life but not directly used in respiration. Additional information : Composition of Air – Approximate %: Nitrogen – 78% Oxygen – 21% Argon – 0.93% Carbon Dioxide – 0.04% Other trace gases (Neon, Helium, Methane, Krypton, etc.) – 0.03%

NOTE: Hydrogen is the lightest gas, but Helium is generally preferred. However, since "Helium" is not listed among your choices, the correct answer from the provided options is Hydrogen Helium is the lightest safe gas commonly used for: Party balloons Advertisement balloons Weather balloons Common MCQ Confusion Hydrogen is actually the lightest gas overall, but it is highly flammable and can catch fire. Helium is slightly heavier than hydrogen but is non-flammable and safe, so it is used in balloon s.

Crystallization (or recrystallization) is the primary technique used for the purification of solid compounds Important points: It is used to remove impurities from solid substances. The impure solid is dissolved in a suitable solvent , then crystals of the pure compound form on cooling. It is commonly used in o rganic chemistry for the purification of solids.

A mixture contains two or more substances physically combined , which can be separated by physical means. Examples include sharbat, tea, steel. Common salt (NaCl) is a pure compound, not a mixture .

Animal cells do not have chloroplasts , as they are not capable of photosynthesis. Animal cells also do not have a cell wall , unlike plant cells and some other organisms. The components of an animal cell : Cell Membrane Cytoplasm Small Vacuole Nucleus Chromosomes

Leaves are called the food factory of plants . They prepare food through the process of Photosynthesis . Chlorophyll in leaves absorbs sunlight to make food. Photosynthesis uses Carbon dioxide (CO₂), Water (H₂O), and Sunlight. Food produced is mainly Glucose , which provides energy to the plant.

Chlorophyll is the green pigment responsible for photosynthesis in plants. It captures sunlight and converts it into chemical energy to make food. Additional information : Plants use chlorophyll to produce glucose and oxygen through photosynthesis . Chloroplasts contain chlorophyll a and b , which absorb sunlight.

Stars produce energy by combining lighter nuclei into heavier nuclei in their cores. In the core of a star, hydrogen nuclei fuse to form helium . This process releases a huge amount of energy in the form of light and heat. It is the primary source of a star’s energy and sustains its radiation for billions of years.

Leaves have thin veins called vascular bundles . Veins consist of xylem and phloem for transport. Xylem transports water and minerals from roots to leaves. Phloem transports food (sugars) from leaves to other parts of the plant.

Phosphorus (P), Potassium (K), and Nitrogen (N) are three essential macronutrients for plant growth. It is also referred to as " NPK ". They play critical roles in various plant processes, including photosynthesis, root development, and cell growth.

A permanent magnet retains its magnetism for a long time. It is hard to magnetize but difficult to demagnetize once magnetized. Made from hard magnetic materials like steel or alnico. Unlike temporary magnets , it does not lose its magnetism easily.

The velocity of a wave depends on its wavelength and frequency . Formula: v = λ × f , where λ is wavelength and f is frequency . This applies to sound waves, light waves, and water waves. Higher frequency or longer wavelength increases the wave’s velocity if the medium is constant.

An echo is a sound that reflects off a surface and is heard again. It occurs when sound waves bounce back from a distant surface like a wall or mountain. Echoes are common in caves, valleys, and empty halls . The reflected sound is perceived after a short delay.

Total internal reflection occurs when light travels from a denser medium to a rarer medium . The angle of incidence must be greater than the critical angle for the two media. Light is completely reflected back into the denser medium instead of refracting . Common examples: optical fibers, diamonds, and mirages.

The sky appears blue due to Rayleigh scattering of sunlight by the atmosphere. Shorter wavelengths like blue light scatter more than longer wavelengths (red, yellow). The scattered blue light reaches our eyes , making the sky appear blue . Red light is less scattered and passes through the atmosphere .

Ions are charged particles formed when an atom gains or loses electrons . Loss of electrons creates a positively charged ion (cation) . Gain of electrons creates a negatively charged ion (anion).

A change in physical appearance or state of a substance , such as a change in shape, size, color, or phase (solid, liquid, gas), is called a Physical Change. The are examples of Physical Changes: Melting (ice cream, wax, chocolate, ice and change from solid to liquid ) Phase changes ( boiling, freezing, condensation ) Crushing (chalk) Tearing (paper) Crumpling (aluminium foil) Stretching (rubber band) Mixing (sugar in water) Dissolving (sugar, salt in water) Moulding (clay, metals) Slicing (fruit) Forming of frost (from water vapors) Transition to a gas (change from liquid to gas) Change of durability (change in texture or strength) Changes to crystal form (change in crystal structure)