Explanation

• 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.

Last verified on 11-03-2026

Explanation

• 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).

Last verified on 11-03-2026

Explanation

• 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.

Last verified on 10-03-2026

Explanation

• 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.

Last verified on 10-03-2026

Explanation

• 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.

Last verified on 10-03-2026

Explanation

• 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.

Last verified on 09-03-2026

Explanation

• 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.

Last verified on 09-03-2026

Explanation

• 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.

Last verified on 09-03-2026

Explanation

• 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

Last verified on 09-03-026

Explanation

• Pressure can be defined as the force acting per unit area.
• The unit of pressure is N/m² (Newton per square meter).
• It is also called Pascal (Pa).
• In SI base units kg⋅m−1⋅s−2
• Derivations from other quantities: p = F / A
• Dimension unit: M L^−1 T^-2.

Additional information 

The SI unit of energy/work is the joule (J)

Last updated on 09-03-2026