Explanation: In fused (molten) sodium chloride, electric current passes due to the presence of free ions. When solid NaCl is melted, it dissociates into Na⁺ and Cl⁻ ions, which can move freely and conduct electricity. In the solid state, these ions are fixed in the crystal lattice, so it does not conduct electricity.

Explanation: Trichology is derived from the Greek word “trikhos”, meaning hair. It is a specialized field within dermatology that focuses on the structure, function, and diseases of hair and scalp. Trichologists diagnose and treat conditions such as hair loss (alopecia), dandruff, scalp infections, and hair shaft disorders.

Common Hair Disorders Studied in Trichology:

• Alopecia: Hair loss due to genetics, stress, or autoimmune disorders.
• Dandruff (Seborrheic dermatitis): Scalp condition causing flaking and itching.
• Tinea capitis: Fungal infection of the scalp (ringworm).

Explanation: The Sun produces its enormous energy through the process of nuclear fusion. In this process, hydrogen nuclei (protons) combine under extremely high temperature and pressure to form helium, releasing a tremendous amount of energy in the form of light and heat. The main fusion reaction in the Sun is the proton–proton chain. Unlike fission (splitting of nuclei), fusion combines light nuclei, and this is what powers all stars, including the Sun.

Explanation: Vitamin B₁₂, also known as Cobalamin, is the only vitamin that contains a metal ion — cobalt (Co) — at its core. It plays a crucial role in red blood cell formation, DNA synthesis, and proper nervous system function. Deficiency of Vitamin B₁₂ leads to pernicious anemia and neurological disorders. It is found mainly in animal-based foods such as meat, eggs, milk, and fish, and is synthesized by certain bacteria.

Explanation: Leguminous crops such as peas, beans, gram, and clover have a symbiotic relationship with Rhizobium bacteria in their root nodules. These bacteria convert atmospheric nitrogen into ammonia, enriching soil fertility naturally. Hence, legumes are used in crop rotation to restore nitrogen content in soil.

Explanation: Acids do not turn red litmus to blue; instead, they turn blue litmus paper red. Acids are sour in taste, corrosive in nature, and have a pH value less than 7. Therefore, the statement that acids turn red litmus to blue is incorrect.

Explanation: Inside a sealed pressure cooker, the pressure is higher than atmospheric pressure, which raises the boiling point of water to about 121℃. This allows food to cook faster because water and steam reach higher temperatures than at normal atmospheric pressure.

Running water is the source of hydel power (also called hydroelectric power). The energy of flowing or falling water is converted into electrical energy using turbines and generators in dams. It is a renewable, clean, and sustainable source of energy widely used in India and worldwide.

• Thermal power: Generated by burning coal or other fuels.
• Nuclear power: Produced from nuclear fission reactions.
• None of the above: Incorrect — running water directly produces hydel power.

Explanation: During photosynthesis, green plants use sunlight to convert carbon dioxide (CO₂) and water (H₂O) into glucose (C₆H₁₂O₆) and oxygen (O₂). The oxygen gas released in this process comes specifically from the splitting of water molecules — a reaction known as photolysis of water, which occurs in the light-dependent reaction inside the chloroplasts.

Chemical equation:

6CO₂ + 12H₂O → C₆H₁₂O₆ + 6O₂ + 6H₂O

The oxygen atoms in the released O₂ come entirely from the original water molecules, as demonstrated by isotopic experiments using heavy oxygen (O¹⁸) tracers.

Explanation: Below the critical temperature, gases can be liquefied by applying pressure because the intermolecular forces of attraction between gas molecules become effective. These forces pull the molecules closer together, resulting in the formation of a liquid state.