IGCSE Chemistry Command Words Decoded

Half the marks students drop on 0620 theory papers are not chemistry errors. They are command-word errors: a correct description written under an “explain” question, a paragraph written where one word was wanted, a calculation shown without working under “determine”. The examiner can only credit what the command word asked for. Learn the 14 words below and you stop donating marks you already earned.

The 14 command words on every 0620 paper

Cambridge defines each command word precisely. Here is what each one pays for.

Command word	What the examiner wants	Typical marks
State	A short factual answer, no reasoning	1
Give	Same as state: a fact, a value or an example	1
Name	The correct chemical name (not formula, unless allowed)	1
Identify	Pick out the right substance/feature, usually from data given	1
Describe	What happens or what something is like: observations, trends	1–3
Explain	Why it happens: reasons, mechanisms, particle/electron-level cause	2–4
Suggest	Apply your chemistry to an unfamiliar case; multiple valid answers	1–2
Calculate	A numerical answer with working shown	1–4
Determine	A numerical or factual answer that must use the data provided	1–3
Deduce	Reach a conclusion from the information given, showing the link	1–2
Predict	Say what will happen in a new situation, based on a pattern	1–2
Compare	Similarities and/or differences between both things, explicitly	2–3
Define	The precise meaning of a term, in syllabus wording	1–2
Sketch	An approximate drawing or graph showing the correct shape/trend	1–2

Each word in action, and where the mark dies

State / Give / Name

Q: State the colour of universal indicator in a strongly acidic solution. (1) A: Red.

One word earns the mark. The classic loss: writing a hedge, “red or maybe orange”. An examiner reads two answers, one right and one wrong, and awards zero. One question, one answer. The second classic loss on “name”: writing a formula when the question says name. “Name the salt formed” wants sodium chloride, not NaCl.

Identify

Q: Identify the gas produced at the cathode. (1) A: Hydrogen.

Identify usually points at the diagram, table or experiment on the page. The mark dies when students answer from memory instead of from the information given, naming a gas that cannot form in that electrolyte.

Describe

Q: Describe what you would see when sodium is added to water. (2) A: The sodium floats and moves across the surface; it melts into a ball and fizzes (effervescence).

Describe means observations: colours, states, fizzing, temperature changes. The mark dies when students write conclusions instead of observations. “Hydrogen gas is produced” is a deduction, not something you see. You see bubbles. Write bubbles.

Explain

Q: Explain why magnesium reacts faster with dilute acid when it is powdered. (2) A: Powder has a larger surface area, so there are more frequent collisions between acid particles and magnesium per second.

Explain is the biggest mark-killer on Paper 4. The mark dies when students re-describe: “the powder reacts faster because it is powdered” earns nothing. Every explain answer needs a because that reaches particles, electrons, bonds or energy. If your answer would still make sense with the word “because” deleted, it is a description, not an explanation.

Suggest

Q: Suggest why the actual yield of the ester is lower than the calculated yield. (1) A: Some product is lost during separation/purification (or the reaction is reversible and does not go to completion).

Suggest signals that the exact answer is not in your notes. The mark dies when students panic and leave it blank. Any chemically reasonable answer scores. Suggest questions have the highest blank rate on 0620 and the most forgiving mark schemes: exactly the wrong combination to skip.

Calculate

Q: Calculate the mass of 0.25 mol of CaCO3 (Mr = 100). (1) A: 0.25 × 100 = 25 g.

The mark dies three ways: no units, wrong rounding, and no working. With working shown, a slip in the final step still collects the method marks on a 3–4 mark calculation. Our mole calculations technique page covers the full layout that protects working marks.

Determine

Q: Determine the relative molecular mass of gas X using the data in the table. (2) A: Working that visibly uses the table values, then the answer with units.

Determine means the route to the answer runs through the data provided. The mark dies when students quote a memorised value or use their own numbers. If the question says “use data from the table” and your answer does not touch the table, expect zero.

Deduce

Q: Deduce the charge on the metal ion in MCl2. (1) A: 2+, because two Cl⁻ ions (each 1−) must be balanced by one 2+ ion.

Deduce wants the conclusion and a visible logical link to the evidence. The mark dies when the conclusion appears without the reasoning chain the question implies.

Predict

Q: Predict whether astatine reacts with iron more or less vigorously than chlorine does. (1) A: Less vigorously, because reactivity decreases down Group VII.

Predict pays for extending a pattern. The mark dies when students state the pattern but never apply it to the new substance. The prediction itself must appear.

Compare

Q: Compare the melting points of sodium chloride and chlorine. (2) A: Sodium chloride has a much higher melting point than chlorine; sodium chloride is a giant ionic lattice with strong electrostatic attractions, whereas chlorine has weak forces between molecules.

Compare must mention both substances. The mark dies when a student writes about one substance only. “Sodium chloride has a high melting point” is half a comparison and earns half the credit at best. Use comparative words: higher, lower, faster, more.

Define

Q: Define relative atomic mass. (1) A: The average mass of the atoms of an element (taking isotopes into account) on a scale where carbon-12 is exactly 12.

Define is the only command word where near-syllabus wording is expected. The mark dies on loose paraphrase: leaving out “average” or the carbon-12 reference turns a definition into a description.

Sketch

Q: Sketch a graph of volume of gas against time for this reaction. (2) A: A curve that is steep at the start, decreases in gradient, and becomes horizontal.

Sketch pays for shape and labels, not artistic precision. The mark dies when the curve never flattens, or when axes are unlabelled.

Worked exam question

Q (Paper 4 style): Aqueous bromine is added to two test tubes. Tube A contains hexane. Tube B contains hexene. (a) Describe what you would see in each tube. (2) (b) Explain the result in tube B. (2)

Model answer: (a) Tube A: the bromine water stays orange (no change). Tube B: the bromine water turns from orange to colourless. (1 mark each: both colours stated, “colourless” not “clear”.) (b) Hexene contains a C=C double bond, so it is unsaturated (1). Bromine adds across the double bond in an addition reaction, forming a colourless dibromo compound (1).

Mark-scheme logic: part (a) is describe: colours only, no reasoning required or credited. Part (b) is explain: the colours earn nothing here; only the double bond and the addition reaction score. Students who write the colour change again in (b) fill the lines and earn zero. This describe/explain pairing appears on nearly every 0620 organic question.

The mistakes that cost marks

1. Explaining a describe, describing an explain. The most reported error in every examiner report. Underline the command word before reading the rest of the question.
2. Two answers on a one-answer line. “Red/orange” or “hydrogen or oxygen”: a wrong answer alongside a right one cancels the mark.
3. Skipping suggest questions. They look unfamiliar by design; the mark schemes accept any sound chemistry.
4. No working under calculate or determine. A bare wrong answer scores zero; wrong answer plus correct method keeps the method marks.
5. One-sided compare answers. If both substances are not named in your answer, you have not compared.

How to phrase it for full marks

Student language: “It reacts faster because the powder is smaller.” Mark-scheme language: “Powder has a larger surface area, so collisions between acid particles and the solid occur more frequently.”

Student language: “The bromine water goes clear.” Mark-scheme language: “The bromine water turns from orange to colourless.” (Clear means transparent; coloured solutions are clear. Colourless is the creditable word.)

Student language: “Sodium chloride has strong bonds.” Mark-scheme language: “Sodium chloride has strong electrostatic forces of attraction between oppositely charged ions, which need a large amount of energy to overcome.”

The pattern: name the particle, name the force, name the consequence. That is also the backbone of the 6-mark extended response technique, where command words decide the whole structure of your answer.

The Malaysia note

Malaysian international-school students sit 0620 in the May/June or October/November series, and the command-word definitions are identical in both. The habit we correct most in the first month of tutoring is SPM-style essay writing carried into IGCSE: long paragraphs under 1-mark “state” questions and thin one-liners under 3-mark “explain” questions. Matching answer length to command word and mark allocation is a 2-3 session fix; it is the first thing we diagnose in a free trial lesson, because it raises a grade without learning any new chemistry. Pair this page with our list of common exam mistakes before your next mock.