FBISE Class 10 Chemistry Practice: Explained MCQs and Reaction Checks

Chemistry revision should help you explain a process, recognise a valid equation and justify an answer. Memorising a letter from an answer key is not enough. If the key contains an error or the options appear in a different order, that approach gives you little protection.

This article provides original practice questions with explanations. It covers selected ideas in acids and bases, equations, equilibrium, redox, organic compounds and chemical calculations. It is a focused study resource, not a complete syllabus or an official FBISE paper.

Check your applicable chemistry assessment framework and teacher’s guidance before deciding which topics belong in your revision plan. The official FBISE framework and model-paper index includes resources with different curriculum and scheme labels. Match those details to your course rather than assuming that a familiar chapter title proves a match.

Use a reason-first revision method

For each question, write your answer and one reason before checking the explanation. If you choose correctly by guessing, record that honestly. A guessed correct answer and an explained correct answer represent different levels of understanding.

When a response is incorrect, identify the type of mistake. Did you confuse a definition, overlook a condition, misread a formula or rely on a wrong remembered answer? Each cause suggests a different follow-up task.

Keep symbolic accuracy separate from verbal familiarity. You might know that magnesium hydroxide neutralises hydrochloric acid but still write the wrong salt formula. Practise both the sentence explanation and the balanced equation so that each supports the other.

Question one: identify the neutralisation product

Magnesium hydroxide reacts with hydrochloric acid. Which salt is formed? A magnesium chloride, B magnesium carbonate, C magnesium sulfate or D magnesium nitrate. Attempt the question before continuing.

The correct answer is A, magnesium chloride. The balanced equation is Mg(OH)₂ + 2HCl → MgCl₂ + 2H₂O. The chloride comes from hydrochloric acid, while the hydroxide and hydrogen ions form water.

Magnesium carbonate would require a carbonate source; it is not produced merely because magnesium hydroxide is used as an antacid. When checking an answer, trace the atoms and ions from the reactants rather than choosing a familiar compound name.

Question two: conserve atoms

Which equation is balanced? A H₂ + O₂ → H₂O, B 2H₂ + O₂ → 2H₂O, C H₂ + 2O₂ → H₂O or D H₂ + O₂ → 2H₂O.

The correct answer is B. The left side contains four hydrogen atoms and two oxygen atoms, and the right side contains the same totals. Option A has two oxygen atoms on the left but only one on the right.

Balance an equation by changing coefficients in front of formulas. Changing H₂O to another formula would change the substance, not simply balance the reaction. After adjusting coefficients, count every element again because a change made for one element can affect another.

Question three: distinguish an acid–base definition

In the Lewis description, a base is an electron-pair donor and an acid is an electron-pair acceptor. Which statement therefore identifies a Lewis base? A it accepts an electron pair, B it donates an electron pair, C it must contain a metal or D it must be a gas.

The correct answer is B. The definition concerns the behaviour of an electron pair. Physical state and the presence of a metal do not define a Lewis base.

Keep this description separate from the Brønsted–Lowry description, which concerns proton transfer. Different definitions can describe related reactions, but swapping their wording creates confusion. Write the name of the definition beside your notes so you know which idea a question is testing.

Question four: understand dynamic equilibrium

For a reversible reaction at dynamic equilibrium in a closed system under constant conditions, which statement is correct? A both reactions stop, B the forward and reverse reaction rates are equal, C reactant and product concentrations must be equal or D all reactants disappear.

The correct answer is B. Forward and reverse reactions continue, but their rates are equal. The concentrations remain constant under those conditions; they do not have to be numerically equal to one another.

A common mistake is treating “constant” and “equal” as if they mean the same thing. Two concentrations can stay unchanged while having different values. Explain this distinction in your own words before moving to numerical equilibrium work.

Question five: identify reduction

Which change directly describes reduction in terms of electrons? A loss of electrons, B gain of electrons, C increase in proton number or D removal of a coefficient from an equation.

The correct answer is B. Reduction is gain of electrons, while oxidation is loss of electrons. In a suitable redox example, Cu²⁺ + 2e⁻ → Cu shows copper ions gaining electrons to form copper atoms.

Check charge as well as atoms in a half-equation. The left side here has overall charge zero because the positive two charge is balanced by two electrons. The copper atom on the right is neutral. This provides a useful consistency check.

Question six: recognise an ether

Which structure has an oxygen atom bonded between two carbon-containing groups? A R–O–R′, B R–OH, C R–COOH or D R–CHO. Here R and R′ represent carbon-containing groups rather than particular named elements.

The correct answer is A, the general arrangement for an ether. Option B represents an alcohol group, option C a carboxylic acid group and option D an aldehyde group in these simplified formulas.

Pay attention to the complete arrangement, not just the presence of oxygen. Several families contain oxygen, but their bonding patterns differ. Drawing the characteristic group can help you distinguish them more reliably than memorising their names in a list.

Question seven: calculate a mass percentage

Using relative atomic masses C = 12, O = 16, N = 14 and H = 1, find the approximate nitrogen mass percentage in urea, CO(NH₂)₂. A 14.0 percent, B 28.0 percent, C 46.7 percent or D 60.0 percent.

The correct answer is C. The relative formula mass is 12 + 16 + 2(14) + 4(1) = 60. Nitrogen contributes twenty-eight of that total, so its mass percentage is (28/60) × 100, approximately 46.7 percent.

The atomic masses are supplied for this exercise. If a question gives different rounding instructions or a reference table, follow those instructions. The method remains the mass contribution of the element divided by the total formula mass, multiplied by one hundred.

Question eight: avoid a formula-reading error

How many oxygen atoms are represented by 3CO₂? A two, B three, C five or D six. The correct answer is D: each carbon dioxide molecule contains two oxygen atoms, and the coefficient represents three such molecules.

Multiply the coefficient by the subscript for the element being counted. The same expression represents three carbon atoms in total. The coefficient applies to the whole formula rather than only the first symbol.

Try a related example: 2Mg(OH)₂ represents two magnesium atoms, four oxygen atoms and four hydrogen atoms. The bracket subscript applies to both oxygen and hydrogen, and the leading coefficient then multiplies every atom in the formula.

Question nine: separate mineral names

Which common mineral is a lead ore? A galena, B haematite, C bauxite or D quartz. The correct answer is A: galena is lead sulfide, PbS. Haematite is an iron ore associated with Fe₂O₃.

This question demonstrates why answer explanations matter. A familiar mineral name can look plausible while referring to the wrong metal. Write a short pair in your notes: galena—lead; haematite—iron, then add the formulas if they are part of your course.

Do not assume that a spelling error in a copied question changes the intended chemistry. If an option is unclear or appears corrupted, check a reliable course reference before memorising either the option or the proposed key.

Check a short explanation

Consider the question: “Why must a chemical equation be balanced?” A weak answer is “because balancing is necessary.” It repeats the demand without explaining it. A clearer answer is that a chemical reaction rearranges atoms, so the equation must show the same number of each type of atom on both sides.

You can support the explanation with an example. In 2H₂ + O₂ → 2H₂O, both sides represent four hydrogen atoms and two oxygen atoms. This connects the general principle with a visible check.

Keep the explanation proportionate to the task. A question asking for a balanced equation needs the equation. A question asking why balancing matters needs the principle as well. Read the command word before deciding what to write.

Build a reaction-checking routine

Start by confirming the formulas of the reactants and proposed products. Next, count the atoms. Then check charge where ions or half-equations are involved. Finally, consider whether the stated conditions and reaction type support the proposed change.

A balanced equation alone does not prove that a reaction occurs as written under every condition. Balancing is a necessary bookkeeping check, while chemical validity also depends on the substances and circumstances. Use your course references for the actual reaction being studied.

When correcting a mistake, keep the original attempt visible. Cross out the incorrect step neatly and add a brief explanation. This lets you see the misconception during later revision instead of facing a page that appears to have been correct from the start.

Practise three short-answer tasks

First, distinguish between equal reaction rates and equal concentrations at equilibrium. Second, explain why the coefficient in 2H₂O does not change water into a different compound. Third, show how the nitrogen percentage calculation for urea uses both the element’s contribution and the total formula mass.

For the first task, state that equilibrium requires equal forward and reverse rates, while constant concentrations may differ in value. For the second, explain that the coefficient changes the represented quantity, whereas the formula still identifies water.

For the third, show twenty-eight divided by sixty, multiplied by one hundred, using the atomic masses given earlier. Writing the calculation without identifying what the two masses represent can hide an incomplete understanding of the method.

Create a chemistry error log

Use columns for concept, original mistake, correct reasoning and retest. An entry might read: “Neutralisation; chose carbonate salt; hydrochloric acid supplies chloride; write and balance a new acid–base equation.” Make the next task specific enough to complete.

During the retest, close the corrected answer. Explain the reasoning before checking it. If you remember only the option letter, change the order of the options or turn the item into a short-answer question.

Review a few errors at a time and include older ones. This helps you check whether a correction lasts beyond the session in which you first saw it. Ask a teacher about unresolved contradictions rather than collecting more unverified answer keys.

Further concept references

For an additional explanation of dynamic equilibrium, see OpenStax Chemistry 2e, Chemical Equilibria. Its treatment supports the distinction between continuing reactions and constant concentrations. The OpenStax discussion of chemical reactions also includes neutralisation. For mineral identification, the University of Minnesota galena page identifies galena as lead sulfide. These references support particular concepts; they do not replace your applicable FBISE course documents.

Use older chemistry notes carefully

The blog’s older chemistry pre-board article needs answer-key corrections and a course review. Until those corrections are made, do not treat that page as an authoritative key. The explained exercises above are new practice material.

For your next session, choose two concepts that caused uncertainty, consult your course explanation and attempt fresh questions. Keep the official assessment index available for checking scope and format. Reliable reasoning is more useful than a large collection of remembered answer letters.