Chemistry: Practice Questions with Answers
Elements, reactions, acids and bases, and materials. Try each question first: tap an option to check it, and the explanation appears below.
Question 1Medium
What is the common laboratory name for a concentrated aqueous solution containing approximately 37% by mass of formaldehyde gas?
Show answerAnswer
✅ A. Formalin
Formalin is the standard laboratory designation for an aqueous solution containing approximately 37 percent formaldehyde by mass, widely utilized as a tissue fixative and biological preservative. Other substances like glyoxal or urotropine represent different chemical derivatives.
Question page →Question 2Easy
What is the chemical formula of washing soda, which is commonly utilized in water softening and glass manufacturing?
Show answerAnswer
✅ A. Sodium carbonate decahydrate
Washing soda is chemically known as sodium carbonate decahydrate, represented by the formula Na2CO3 dot 10H2O. Sodium bicarbonate is baking soda rather than washing soda. Sodium hydroxide is caustic soda and causes severe chemical burns. Sodium chloride is common table salt and does not form a decahydrate crystal lattice under standard conditions. Solvay process is the primary industrial method employed for producing sodium carbonate on a large commercial scale.
Question page →Question 3Medium
Which noble gas is most abundant in Earth's atmosphere by volume after nitrogen, oxygen, and argon?
Show answerAnswer
✅ A. Neon
Neon is the most abundant noble gas in the Earth's atmosphere after argon, accounting for approximately 0.0018 percent by volume. Other options like helium and krypton exist in lower concentrations of about 0.0005 percent and 0.0001 percent respectively, while xenon is even scarcer. Nitrogen constitutes the largest share of the atmosphere at roughly 78 percent. Noble gases are chemically inert and grouped in Group 18 of the periodic table.
Question page →Question 4Easy
Which acid present in ant stings causes pain, swelling, and a burning sensation on human skin?
Show answerAnswer
✅ A. Methanoic acid
Methanoic acid, universally recognized as formic acid, is injected by ants during stings, triggering localized inflammation, pain, and itching on human skin. Other acids like acetic acid constitute the primary component of vinegar rather than insect venoms. Neutralizing such stings typically requires weak alkaline substances like baking soda.
Question page →Question 5Medium
Which of the following functional groups characterizes secondary alcohols?
Show answerAnswer
✅ B. >CHOH
Secondary alcohols are characterized by a hydroxyl group attached to a carbon atom that is bonded to two distinct alkyl or aryl groups, represented by the general structural formula >CHOH. The -CH2OH group defines primary alcohols, whereas the carbonyl group >C=O is typical of aldehydes and ketones.
Question page →Question 6Medium
Consider the following statements about bleaching powder: 1. It is chemically prepared by passing chlorine gas over dry slaked lime. 2. It acts as an oxidizing agent in many chemical industries. Which of the statements given above is/are correct?
Show answerAnswer
✅ C. Both 1 and 2
Bleaching powder is manufactured commercially by the action of chlorine gas produced during the chlor-alkali process on dry calcium hydroxide, yielding calcium oxychloride. It functions effectively as a powerful oxidizing agent due to the release of active chlorine in aqueous solutions, making it useful for disinfecting drinking water and bleaching textiles. Incorrect choices miss one of these standard industrial preparation or reactivity facts. Bleaching powder gives off a strong smell of chlorine because it reacts slowly with atmospheric carbon dioxide.
Question page →Question 7Easy
Which gas is evolved when zinc metal reacts with dilute sulfuric acid?
Show answerAnswer
✅ A. Hydrogen
Active metals situated above hydrogen in the reactivity series displace hydrogen gas when they react with dilute mineral acids like sulfuric acid. This single displacement reaction yields aqueous zinc sulfate alongside bubbles of flammable hydrogen gas. Such chemical reactions demonstrate the reducing behavior of metals in acidic environments.
Question page →Question 8Hard
Consider the electrochemical cell represented by standard zinc and copper half-cells. Which of the following changes will lead to an increase in the cell potential measured under non-standard conditions according to the Nernst equation?
Show answerAnswer
✅ C. Increasing the concentration of copper ions in the cathode compartment
According to the Nernst equation for a galvanic cell, the cell potential increases when the concentration of reactant products decreases or when the concentration of reactants in the cathode reduction half-reaction increases, such as raising copper ion concentration. Increasing zinc ion concentration at the anode or decreasing copper ions would shift the reaction quotient and lower the net cell voltage. Standard cell potential is an intensive property and does not depend on the stoichiometric coefficients used to balance the redox equation.
Question page →Question 9Medium
Which metal is obtained during the reduction of bauxite ore via the Hall-Héroult electrolytic process?
Show answerAnswer
✅ C. Aluminum
The Hall-Héroult process serves as the principal industrial route for smelting pure aluminum from dissolved bauxite ore in a molten cryolite bath. Iron extraction relies on blast furnace reduction using coke, whereas copper extraction involves smelting sulfide ores. Aluminum production requires high electrical energy consumption, making proximity to cheap power sources vital for smelting plants.
Question page →Question 10Easy
Which element is the most abundant by mass in the Earth's crust?
Show answerAnswer
✅ C. Oxygen
Oxygen is the most abundant chemical element by mass in the Earth's crust, accounting for approximately forty-six percent of its total composition, largely combined in silicate minerals. While silicon is also highly prevalent, it ranks second behind oxygen in crustal abundance by mass. Questions regarding elemental abundances in the lithosphere form a standard part of physical geography and general science syllabi.
Question page →Question 11Easy
Which gas is commonly known as 'laughing gas' and is used as a medical anesthetic and analgesic?
Show answerAnswer
✅ B. Nitrous oxide
Nitrous oxide, chemically represented as N2O, is widely known as laughing gas due to its euphoric effects upon inhalation and finds extensive application as a medical anesthetic and analgesic in clinical procedures. Nitric oxide and nitrogen dioxide are toxic air pollutants associated with industrial combustion and photochemical smog rather than safe medical use.
Question page →Question 12Hard
What is the primary intermediate species formed during the Reimer-Tiemann reaction when phenol is treated with chloroform in the presence of an aqueous sodium hydroxide base?
Show answerAnswer
✅ A. Dichlorocarbene electrophile
The Reimer-Tiemann reaction proceeds via the alpha-elimination of hydrogen chloride from chloroform induced by strong base to generate a reactive dichlorocarbene electrophile that attacks the phenol ring. Free radicals are involved in halogenation reactions rather than carbene insertions. Diazonium ions are formed during aniline diazotization. Carboxylate ions are formed during carboxylation procedures like the Kolbe reaction.
Question page →Question 13Easy
Which acidic reagent, comprising a 3:1 mixture of concentrated hydrochloric acid and concentrated nitric acid by volume, can dissolve noble metals such as gold?
Show answerAnswer
✅ A. Aqua Regia
Aqua Regia is a highly corrosive, fuming mixture prepared by combining concentrated hydrochloric acid and concentrated nitric acid in a 3:1 volumetric ratio, capable of dissolving noble metals like gold. Other mixtures like Bordeaux Mixture are agricultural fungicides rather than precious metal solvents.
Question page →Question 14Medium
Which of the following polymers is a naturally occurring condensation polymer?
Show answerAnswer
✅ C. Protein
Proteins are naturally occurring condensation polymers formed via peptide linkages between amino acid monomers with the release of water molecules. Synthetic polymers like polyethylene and PVC are produced artificially through addition or condensation polymerization in industrial settings. Polymer chemistry is a regular topic in competitive science tests.
Question page →Question 15Medium
In the extraction of iron from its oxide ores in a blast furnace, what is the primary role of limestone added to the charge?
Show answerAnswer
✅ B. To decompose into calcium oxide and flux acidic silica impurities forming slag
Limestone decomposes thermally inside a blast furnace to form calcium oxide, which acts as a basic flux reacting with acidic silica impurities present in the ore to form molten calcium silicate slag that floats on liquid iron. Carbon monoxide serves as the primary reducing agent, and coke provides thermal energy. Slag removal protects the molten metal from reoxidation.
Question page →Question 16Medium
Which of the following laws states that the solubility of a gas in a liquid is directly proportional to the partial pressure of the gas above the liquid?
Show answerAnswer
✅ B. Henry's law
Henry's law establishes that the solubility of any given gas in a liquid at constant temperature varies in direct proportion to the partial pressure exerted by that gas above the solution. Distractors like Raoult's law deal with vapor pressure lowering in liquid-liquid mixtures rather than gas dissolution. This scientific principle accounts for the behavior of carbonated beverages and deep-sea diving breathing gases.
Question page →Question 17Medium
Which allotrope of carbon is structured as a layered planar network of hexagonally arranged carbon atoms where each carbon is bonded to three others, imparting electrical conductivity?
Show answerAnswer
✅ B. Graphite
Graphite consists of sp2 hybridized carbon atoms arranged in planar sheets held together by weak van der Waals forces, allowing layers to slide and electrons to move freely. Diamond is sp3 hybridized in a rigid tetrahedral lattice making it an electrical insulator. Fullerenes form discrete spherical cage molecules containing pentagonal and hexagonal rings.
Question page →Question 18Hard
What is the principal reason why transition metals exhibit variable oxidation states in their chemical compounds?
Show answerAnswer
✅ B. The very small energy difference between (n minus 1) d-orbitals and ns-orbitals
Transition elements possess valence electrons in both the outermost s-orbital and the penultimate d-orbital. Because the energy difference between these orbitals is remarkably small, electrons from both levels can participate in chemical bonding, allowing atoms to exhibit multiple stable oxidation states. Large electronegativity or complete shielding would prevent this flexible electron participation. Variable oxidation states allow transition metal ions to function effectively as homogeneous and heterogeneous catalysts.
Question page →Question 19Medium
What is the common name for trichloromethane, which was historically used as an early general anesthetic?
Show answerAnswer
✅ C. Chloroform
Chloroform is the common chemical term for trichloromethane, a dense, colorless liquid that historically served as an early general anesthetic in medical surgeries before safer alternatives were developed. Its inhalation depresses the central nervous system, though toxicity risks led to its discontinuation in modern clinical practice.
Question page →Question 20Medium
Which among the following is a condensation polymer commonly used in the manufacture of magnetic recording tapes and synthetic fibers?
Show answerAnswer
✅ C. Dacron (Terylene)
Dacron, also known as Terylene, is produced via condensation polymerization between ethylene glycol and terephthalic acid, releasing water molecules as a byproduct. In contrast, polymers like polyethylene are formed through addition polymerization without byproduct elimination. Terylene fibers possess high crease resistance and strength, making them ideal for blended textile manufacturing.
Question page →
Ready to test yourself against the clock?
⏱️ Take a timed Chemistry test →New questions every time, with your score saved to My progress.
More General Science practice