General Science MCQs – Page 31 (Q301-310)

The chemical formula for water is H2O, indicating that each water molecule consists of two hydrogen atoms covalently bonded to one oxygen atom, arranged in a bent, V-shaped geometry due to the two lone electron pairs on the oxygen atom. This bent shape makes water a polar molecule, meaning it has a slightly negative end near the oxygen and slightly positive ends near the hydrogens, which allows water molecules to form hydrogen bonds with one another, giving water its unusually high boiling point, surface tension, and ability to act as an excellent solvent, often called the universal solvent, for countless substances.

The chemical formula for carbon dioxide is CO2, indicating that each molecule consists of one carbon atom double-bonded to two oxygen atoms in a linear arrangement. Carbon dioxide is produced by cellular respiration in living organisms and by the combustion of fossil fuels, and it is absorbed by plants during photosynthesis to produce glucose and oxygen. As a greenhouse gas, carbon dioxide traps heat within Earth's atmosphere, and its rising atmospheric concentration due to human activities since the industrial revolution is the primary driver of contemporary climate change, making its chemical formula one of the most frequently referenced in modern environmental science.

The chemical formula for common table salt is NaCl, sodium chloride, formed when a sodium atom loses one electron to become a positively charged sodium ion and a chlorine atom gains that electron to become a negatively charged chloride ion, with the two oppositely charged ions then held together by strong electrostatic attraction in an ionic bond. This ionic bonding produces salt's characteristic crystalline structure and high melting point, and unlike the two dangerously reactive elements from which it forms, sodium metal and chlorine gas, the resulting compound is stable, non-reactive, and essential for human health, used both as a seasoning and a critical electrolyte in the body.

The chemical formula for methane, the main component of natural gas, is CH4, indicating one carbon atom covalently bonded to four hydrogen atoms in a symmetrical tetrahedral shape, the simplest possible hydrocarbon. Methane is a colorless, odorless gas, though natural gas suppliers deliberately add a sulfur-based odorant so leaks can be detected by smell for safety. As a potent greenhouse gas, methane traps significantly more heat per molecule than carbon dioxide over a short timeframe, though it breaks down in the atmosphere much faster, and it is produced naturally by decomposing organic matter, livestock digestion, and released from fossil fuel extraction.

The chemical formula for ammonia is NH3, indicating one nitrogen atom covalently bonded to three hydrogen atoms in a pyramidal shape, with a lone electron pair on the nitrogen giving the molecule its characteristic reactivity and pungent, sharp odor. Ammonia is industrially produced on a massive scale through the Haber-Bosch process, which combines atmospheric nitrogen with hydrogen under high pressure and temperature using a catalyst, a process critical for manufacturing synthetic nitrogen fertilizers that support much of modern global agriculture and food production. Ammonia is also used in household cleaning products and, in its liquid form, as a refrigerant.

The chemical formula for sulfuric acid is H2SO4, one of the most widely produced industrial chemicals worldwide, consisting of two hydrogen atoms, one sulfur atom, and four oxygen atoms, and considered a strong acid because it fully dissociates in water to release hydrogen ions. Sulfuric acid is used extensively in fertilizer production, petroleum refining, and as the electrolyte in lead-acid car batteries, and it is highly corrosive, capable of causing severe chemical burns and reacting violently, and dangerously exothermically, when concentrated acid is added carelessly to water rather than the correct, safer practice of slowly adding acid to water.

The chemical formula for hydrochloric acid is HCl, a strong acid formed when hydrogen chloride gas dissolves in water, fully dissociating into hydrogen ions and chloride ions in solution. Hydrochloric acid occurs naturally in the human stomach, where it is secreted at low concentrations to aid digestion by breaking down food and activating digestive enzymes like pepsin, while also killing many ingested harmful bacteria. Industrially, hydrochloric acid is widely used in metal cleaning, called pickling, chemical manufacturing, and food production, and it is also commonly used in school and college chemistry laboratories to demonstrate fundamental acid-base reactions.

The common chemical formula for baking soda, or sodium bicarbonate, is NaHCO3, a mild base widely used in cooking as a leavening agent, since it reacts with acidic ingredients like vinegar, buttermilk, or lemon juice to release carbon dioxide gas, causing batters and doughs to rise. Beyond baking, sodium bicarbonate is used as a gentle antacid to neutralize excess stomach acid, as a natural deodorizer to absorb odors, and as a mild abrasive cleaning agent, reflecting its versatility as a safe, inexpensive, and mildly alkaline compound found in countless household applications.

The chemical formula for glucose, a simple sugar, is C6H12O6, a monosaccharide that serves as the primary energy source for most living cells, produced by plants during photosynthesis from carbon dioxide and water using light energy, and broken down by cells during cellular respiration to release usable chemical energy in the form of ATP. Glucose circulates in the bloodstream of animals as blood sugar, tightly regulated by hormones like insulin and glucagon, and its concentration is a critical health indicator, particularly in the diagnosis and management of diabetes mellitus, a condition involving impaired blood glucose regulation.

The chemical formula for ozone is O3, a molecule consisting of three oxygen atoms, distinguishing it from the more common diatomic oxygen molecule, O2, that makes up most of the oxygen in the air we breathe. Ozone concentrated in the stratosphere forms a protective layer that absorbs most of the Sun's harmful ultraviolet radiation, shielding life on Earth's surface, while ground-level ozone, formed through reactions involving vehicle emissions and sunlight, acts as a harmful air pollutant and a component of smog. This dual nature, beneficial in the stratosphere but harmful at ground level, makes ozone a frequently tested concept in environmental science.