Explanation

• Oxygen has 8 protons and typically 8 neutrons, giving it a mass number of 16.
• Mass number = Number of protons + Number of neutrons.
• Discoverers: Joseph Priestley, Carl Wilhelm Scheele
• Symbol: O
• Atomic number: 8
• Electrons per shell: 2, 6
• Discovered: 1774

Explanation

The valency of both hydrogen and potassium is 1.  

Hydrogen (H):

- Atomic number = 1 → has 1 electron.

- Needs 1 more to complete its outer shell → shares or loses 1.

- So, its valency is +1.

Potassium (K):

- Atomic number = 19 → 1 electron in outer shell.

- Easily loses 1 electron to become stable → forms K⁺.

- So, its valency is +1.

Explanation

Solids:

• Have a definite shape and volume.
• Their particles are tightly packed and vibrate in fixed positions.

Liquids:

• Have a definite volume but take the shape of their container.
• Their particles are close but can move past one another.

Gases:

• Have no definite shape or volume and expand to fill their container.
• Their particles are far apart and move freely. 

Explanation

Reflecting telescope: uses a concave mirror (primary) and a plane mirror (secondary).

• Concave mirror collects/focuses light.
• Plane mirror directs it to the eyepiece.
• No chromatic aberration; can be built larger than lenses.

Explanation

• Atoms are made up of subatomic particles.
• The three main particles are protons, neutrons, and electrons.
• Protons have a positive charge.
• Electrons have a negative charge.
• Neutrons have no electric charge.

Explanation

• Chlorine is used to kill harmful bacteria.
• This process is called chlorination.
• One of the most common methods of water disinfection. 
• Chlorine is effective because it:
• Kills or inactivates disease-causing microorganisms, such as bacteria, viruses, and parasites.
• It is relatively inexpensive and easy to apply.
• While other methods like ozone and ultraviolet (UV) light are also used for disinfection

Explanation

• Water covers approximately 71% of the Earth's surface.

Additional information

• Land Coverage: The remaining 29% of the Earth's surface consists of land, including continents and islands.
• Water Distribution: About 96.5% of Earth's water is held in the global oceans as saltwater

Explanation

The assumption that is NOT made: "No external forces acting on the fluid"

• Bernoulli's equation requires gravity to be present and acting on the fluid.
• The height/head term ($\rho gh$) in the equation is derived from the work done by gravity. Without gravity, this term would not exist.

Additional information

• Steady flow — Properties at any point stay constant over time.
• Incompressible fluid — Density (ρ) is constant.
• Negligible viscosity — The fluid is inviscid/frictionless, so no shear forces or turbulence along the streamline.

Explanation

• The Clausius–Clapeyron equation relates vapor pressure and temperature.
• It describes how vapor pressure changes with temperature.
• It is commonly used for liquid–vapor equilibrium.
• It involves the enthalpy of vaporization.
• As temperature increases, vapor pressure generally increases.

Explanation

Water treatment removes or reduces harmful pollutants.

Treatment may involve:

• Sedimentation: Heavy clumps settle to the bottom of the water supply.
• Filtration: Clear water passes through filters of sand, gravel, and charcoal to remove remaining particles.
• Disinfection: Chlorine or UV light is added to kill harmful bacteria and germs.