TL;DR:
Cover the choices and answer the question yourself first. The choices are designed to tempt you.
Then eliminate options that cannot be right, and compare what is left against the question again.
Flag questions that take too long and return to them, so one hard item does not cost you the easy ones after it.
Multiple-choice questions look easy because the right answer is on the page. That is also the trap. The wrong options are written to look like what a hurried or half-prepared student would pick. If you read the choices first, you start comparing them with each other instead of with the chemistry in your head.
A good strategy is mostly about order: think first, then look, then eliminate.
Why the order matters
When you read options before thinking, each plausible-looking one plants an idea. You then judge each by whether it "feels familiar", and familiarity is exactly what distractors are built to produce. When you produce your own answer first, you compare the options against something solid.
What you need
A piece of scrap paper or the margin, if allowed.
A way to flag questions, such as a circle on the question number.
A rough time per question. See the first five minutes of any exam.
The steps
Cover the choices and read the stem: Read only the question. Underline what it asks, including words like NOT, EXCEPT or ONLY.
Answer it yourself: Work it out or state it in your own words before you look at the options.
Look at the choices: See if your answer is there. If it is, check one more time that nothing better matches.
Eliminate: If not, cross out options that are impossible, such as the wrong units, the wrong sign, or something that contradicts the stem.
Flag and move on: If you are still unsure after about a minute, pick your best guess, flag it and go on.
Worked example: eliminating answers on a chemistry question
What is the pH of a 0.010 M solution of hydrochloric acid, HCl? The options are A) 1, B) 2, C) 7, D) 12.
Cover the choices and answer. HCl is a strong acid, so it dissociates completely. That makes [H⁺] = 0.010 M = 1.0 × 10⁻² M. Then pH = −log(1.0 × 10⁻²) = 2. Now look at the choices: B says 2.
If you could not do the calculation, eliminate. The solution is an acid, so the pH must be below 7. That removes C (neutral) and D (12 is basic). Two options remain: 1 and 2. Think about what each number means: pH 1 corresponds to a hydrogen ion concentration of 0.1 M, while pH 2 corresponds to 0.01 M. The question says 0.010 M, so it is B.
Check the distractors. A, pH 1, is what you would get from a 0.10 M solution, a classic slip of one power of ten. D, pH 12, is the pH of a 0.010 M solution of a strong base such as NaOH, where pOH = 2 and pH = 14 − 2 = 12. Both are tempting if you grab a number you remember. Because you answered first, you were not pulled by either.
Questions with no calculation
For conceptual stems, do the same thing in words. "Which statement best explains why ice floats?" Before looking, say: "It is less dense because of the open structure of hydrogen-bonded water molecules." Then find the option that matches in meaning, even if worded differently.
Flag and return
Hard questions can eat time. Give each about a minute or less than the time you budgeted, make your best choice, circle the number and move on. When you come back, you may see the problem differently, or a later question may remind you of the trick. Check the rules for whether a wrong answer loses marks. If it does not, never leave a blank.
When you come back to flagged questions, change an answer only if you can say why. A new reading of the question or a found slip is a good reason. A vague feeling is not.
Reading the stem closely
Most of the traps in multiple choice are in the stem. Words like NOT, EXCEPT, ONLY, ALWAYS and BEST change the whole question. Underline them as you read. A question that asks which statement is NOT true is answered by finding three true statements, so work in that direction and check each option against the idea in the stem.
Numbers and units are traps too. If options differ by a factor of ten or by the units, such as m/s against km/h, convert before you compare. Many wrong options are right answers to a slightly different question.
Mistakes to avoid
Reading all four choices before thinking.
Missing words like NOT or EXCEPT in the stem.
Choosing an option because it is longer or sounds more technical.
Spending several minutes on one question.
Changing answers at the end without a reason.
Your plan for this week
On your next set of practice questions, cover the choices on every one and write your own answer first.
Mark whether your answer matched an option.
For misses, note which distractor you were drawn to and why.
Practise flagging: set a one-minute limit on each question.
Frequently asked questions
What if my own answer is not among the options?
Reread the stem for a missed word and check your arithmetic. If you still disagree, eliminate what is clearly wrong and choose the closest remaining option.
Is it true that I should keep my first answer?
Not as a rule. Keep it unless you find a specific reason to change, such as an error you can name.
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