Every "important topics" list for O/L Science says roughly the same things, and none of them show their working. So we did the count. Wizder has curated 500 multiple-choice questions from 13 O/L Science past papers (Paper I, 2013 to 2025), each one tagged with the specific thing it tests. Here is what 13 sittings actually repeat.
The headline: the paper repeats far less than you think
Across those papers the questions carry 437 distinct topic tags. 384 of them (88%) appear in exactly one sitting. Only 14 appear in three or more different years. There is no topic that shows up in every single paper.
What that means in practice: chasing a short list of "guaranteed" topics is a bad bet on Paper I. The paper is built to spread across the syllabus. The repeating topics below are worth doing first, not worth doing only.
The newest sittings in that count each have their own page: the 2025 O/L Science paper, the 2024 paper and the 2023 paper. What the 2025 paper asked, and what to do with it for the next exam, is in what the 2025 O/L Science paper tested. Every sitting is on the O/L Science past papers page.
The topics that come back most often
Ranked by the number of different sittings a topic appears in, which is a better signal than raw question count: two questions in one year is a busy paper, two questions in two years is a pattern.
| # | Topic | Years it appeared in | Questions |
|---|---|---|---|
| 1 | ප්‍රභාසංශ්ලේෂණය | 6 of 13 | 7 |
| 2 | මවුල සංකල්පය | 5 of 13 | 5 |
| 3 | ප්‍රවේණික ආබාධ | 3 of 13 | 4 |
| 4 | ආලෝක වර්තනය | 3 of 13 | 3 |
| 5 | තරල පීඩනය | 3 of 13 | 3 |
| 6 | ද්විපද නාමකරණය | 3 of 13 | 3 |
| 7 | පාරිසරික පිරමිඩ | 3 of 13 | 3 |
| 8 | ප්‍රවේග-කාල ප්‍රස්තාර | 3 of 13 | 3 |
| 9 | බහිස්ස්‍රාවය | 3 of 13 | 3 |
| 10 | විද්‍යුත් චුම්බක ප්‍රේරණය | 3 of 13 | 3 |
| 11 | වෙන් කිරීමේ ක්‍රම | 3 of 13 | 3 |
| 12 | සම්ප්‍රයුක්ත බලය | 3 of 13 | 3 |
| 13 | සහසංයුජ බන්ධන | 3 of 13 | 3 |
| 14 | සෛල ඉන්ද්‍රියිකා | 3 of 13 | 3 |
| 15 | අම්ල උදාසීන කිරීම | 2 of 13 | 2 |
How to use this list
- Start at the top and do that topic's questions from every year it appears in. Seeing the same idea asked four different ways is worth more than four readings of one page.
- Then stop using this list and use your own: the questions you get wrong are a better revision plan than any topic ranking, including this one.
Method, so you can argue with it
One tag per question, assigned during curation and checked against the marking scheme alongside the answer. Tags are specific on purpose ("fluid pressure", not "physics"), which is why the distinct-tag count is high and why two questions about the same broad unit can carry different tags. A coarser tagging scheme would produce a shorter list and a friendlier headline, and would tell you less. Paper II is not included: it is not multiple choice, and this count is about Paper I.
One of them, in full
කොපුල් සෛල ආලෝක අණ්වීක්ෂය යටතේ නිරීක්ෂණය කළ විට දැකිය හැකි ඉන්ද්‍රියිකාවක් වන්නේ
- Aගොල්ගි සංකීර්ණය ය.
- Bමයිටොකොන්ඩ්‍රියම ය.
- Cන්‍යෂ්ටිය ය.
- Dරයිබොසෝම ය.