Explanation: Natural gas is a non-renewable source of energy because it is formed from fossilized organic matter over millions of years and cannot be replenished quickly. In contrast, geothermal energy, flowing water, and biomass are renewable as they can be naturally regenerated over short periods.

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

Explanation: An alpha particle (α-particle) is a positively charged particle that consists of two protons and two neutrons, the same as the nucleus of a helium atom (He²⁺). It carries a +2 charge because of the two protons and has a mass number of 4. Alpha particles are emitted during the radioactive decay of heavy elements such as uranium, radium, and thorium. They have high ionizing power but low penetration ability and can be stopped by a sheet of paper or human skin.

The normal hearing range of human beings is from 20 Hz to 20,000 Hz (20 kHz). Sounds below 20 Hz are called infrasonic sounds, while those above 20,000 Hz are known as ultrasonic sounds, both of which are inaudible to humans. With age or prolonged exposure to loud noise, the upper hearing limit tends to decrease, reducing sensitivity to high-frequency sounds.

Other options (for context)

• 30 to 30,000 Hz: Incorrect — exceeds the upper audible limit for humans.
• 50 to 50,000 Hz: Incorrect — animals like dogs and bats can hear this range, not humans.
• 40 to 40,000 Hz: Incorrect — the human ear cannot detect frequencies that high.

The ozone hole leads to an increase in ultraviolet (UV) radiation reaching the Earth's surface. The depletion of the ozone layer, caused by chemicals like CFCs (chlorofluorocarbons), reduces its ability to block harmful UV rays. This can result in health issues such as skin cancer, cataracts, and also harm to crops and marine ecosystems.

• Acid rain: Caused by sulphur and nitrogen oxides, not ozone depletion.
• Global warming: Caused by greenhouse gases trapping heat.
• Greenhouse effect: Natural process intensified by CO₂, not related to ozone loss.

The highest tides, known as spring tides, occur during the time of the new moon and the full moon. During these phases, the Sun, Moon, and Earth are aligned in a straight line, causing their combined gravitational forces to produce higher high tides and lower low tides. This alignment amplifies the tidal effect, resulting in the strongest tidal ranges.

Other options (for context)

• Solar eclipse: Can coincide with a new moon but is not directly responsible for higher tides.
• Lunar eclipse: Occurs during a full moon but does not always produce exceptionally high tides.
• Volcanoes: Have no relation to tidal movements; tides are caused by gravitational forces, not geological activity.

Explanation: Haemoglobin is a complex iron-containing protein found in red blood cells (RBCs). It binds with oxygen in the lungs to form oxyhaemoglobin and releases it in tissues where oxygen levels are low. It also helps transport carbon dioxide from tissues back to the lungs. This oxygen-carrying property makes haemoglobin the essential respiratory pigment in humans and most vertebrates.

Explanation: Plants absorb nitrogen from the soil mainly in the form of nitrates (NO₃⁻). Inside the plant, nitrates are reduced to nitrites (NO₂⁻) and then to ammonia (NH₃) through the action of specific reductase enzymes. The ammonia thus formed is then used to synthesize amino acids, proteins, nucleic acids, and other nitrogen-containing compounds necessary for plant growth.

Simplified Pathway:

NO₃⁻ → NO₂⁻ → NH₃ → Amino acids → Proteins

Explanation: When salt is added to pure water, its boiling point increases. This phenomenon is known as boiling point elevation, a colligative property. The presence of dissolved salt particles reduces the vapor pressure of water, requiring a higher temperature for it to boil.