Explanation

• The freezing point of heavy water is 3.82°C:
• Heavy water (D2O) Regular water
• Freezing point 3.82°C 0°C |
• Boiling point 101.42°C 100°C | 
• Heavy water is made up of two deuterium atoms and one oxygen atom.
• It contains more deuterium, a hydrogen isotope, than regular water, which contains hydrogen-1.
• Heavy water is used in reaction mechanisms.
• It is is prepared by electrolyzing water.

Last verified on 30-03-2026

Explanation

• 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

Last verified on 19-03-2026

Explanation

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.

Last verified on 19-03-2026

Explanation

• 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.

Last verified on 19-03-2026

Explanation

• 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.

Last verified on 19-03-2026

Explanation

• 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.

Last verified on 19-03-2026

Explanation

• 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.

Last verified on 18-03-2026

Explanation

• 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%

Last verified on 18-03-2026

Explanation

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 balloons.

Last verified on 18-03-2026

Explanation

• 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 organic chemistry for the purification of solids.

Last verified on 18-03-2026