Read the rule before answering
A prefix can make a symbol longer without creating another SI base unit. Start with the seven rows in the BIPM base-unit table; count the letters in the unit-symbol column, not the quantity symbol or the unit’s written name.
Six untimed questions, starting with this one.
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Read the lesson — reveals answers & strategy
Understand the boundary
The qualifying units are kilogram (kg), mole (mol) and candela (cd). The other four unit symbols—s, m, A and K—each have one letter. Kilogram is itself the named SI base unit of mass, even though its name includes kilo. That exception does not make kilometre or milligram another base unit.
Verify the facts: BIPM · SI base units and quantities ↗
Choose an answer for your goal
The fixed scores are 35 for kilogram, 75 for mole and 95 for candela. Full names, their listed plurals and kg, mol and cd are accepted. Case-insensitive matching is a game input convenience, not permission to change capitalization in scientific writing. A quantity such as mass or a chemical element is not a unit.
Worked examples — reveals answers
- kg · Accepted
- Kilogram is a row in the base-unit table and its official symbol has two letters.
- moles · Accepted
- A listed plural of mole; mol has three letters. The typed name does not need to have three letters.
- metre · Outside this set
- It is a base unit, but its symbol m has only one letter.
- km · Outside this set
- Kilometre has a two-letter symbol but is a prefixed multiple of metre, not a separate base unit.
- newton · Outside this set
- A derived unit of force, outside the seven base units.
Practice the distinction
Predict the results for km, kg and metre, giving a separate membership and symbol-length reason for each. Then submit a full qualifying unit name and its symbol and verify that they return the same points.
Try it in the checker ↑Check the evidence
Sources checked 2026-10-22 UTC with Codex assistance. Facts establish eligibility; the points belong to our independent practice edition.
Give me a hint — no answer revealed
Start with the full category, then apply the exact boundary: The seven SI base units in the BIPM table. Count letters in the unit symbol, not its name. Names, plurals or the exact symbols kg, mol and cd count. You only need one qualifying answer. A longer name is not automatically rarer.
Reveal a verified practice pick
This pick belongs to the selected question’s answer set. Points are a fixed knowledge rating.
Reveal a fast high-scoring answer
Shortest accepted input at 65+ points
cdCandela · 95 points · 2 characters
Candela is the SI base unit of luminous intensity. Its symbol, cd, has two letters, so it meets the more-than-one-letter rule.
Highest fixed score
Candela95 points · Shortest accepted spelling: cd
These are editorial points, separate from real player choice counts.
Reveal all 3 practice answers
Filter by a name or listed alias. Scores are fixed knowledge ratings.
3 accepted answers
No answers match these filters. Try another spelling or a lower minimum score.
Source review: answer set retained
Reviewed . The BIPM table supports the existing answer set. The question, accepted spellings and fixed scores remain unchanged, including older shared dives.
All 12 reports available at review time were examined: 10 were outside the stated rule and 2 need clarification. No missing eligible answer was confirmed. Submitters can read their individual decision and add evidence in My reports.
Read the review evidence and limits
2026-09-22–2026-10-21 UTC: 381 recorded rounds for this question. Only 265 have complete diagnostic fields; the other 116 are excluded from the following rates.
- 35 accepted · 196 timed out · 34 skipped, out of 265 diagnosed rounds.
- 162 rounds had at least one rejected attempt; 6 of those eventually ended with an accepted answer. These counts overlap the final outcomes above.
- 324 rejected attempts were counted. The game does not retain the text of every rejected attempt; submitted reports are a self-selected subset.
The diagnostic timeout rate was 74.0%. This flags a question for investigation; it does not establish the cause of each timeout. Reports were reviewed up to 2026-10-22 UTC, beyond the diagnostic window.
Action: explain base units versus prefixes and derived units, and provide untimed practice. Compare later rounds for this exact question once at least 20 new diagnosed rounds are available, using timeout, rejection and recovery together. This historical window cannot measure the effect of the new lesson.
Review method: source checks and validator checks by Codex; not an independent human audit. Retained answer version: a1-8d0bc309. Any future answer, rule or score correction must publish a new version and preserve this edition.
What players actually choose
– UTC · 381 recorded daily rounds. Source: Krillionio daily submissions. Skips and timeouts are included in the denominator; practice and Battle are excluded.
60 / 381 rounds ended with an accepted answer (15.7%). Average: 7.9 fixed points.
Compare observed choices — reveals answers
Question quality signals
These measurements cover completed daily rounds recorded with timing and rejection details. Older rounds without those fields are excluded. At least 20 measured rounds are required per question.
Review thresholds: below 20% accepted, at least 40% timed out, or at least 30% of rounds with an unlisted input. These flags suggest checking the wording and answer coverage; they do not prove an answer is wrong or change points automatically. Abandoned rounds and practice attempts are not included.
Answer comparisons require 5 choices and 20 rounds for the same question. These are anonymous browser records, not verified unique people or a representative survey. The index does not change game points or predict the original Krillion game. Read the method and limitations → Inspect aggregate data (JSON) →
Rule examples & common mix-ups — may reveal answers
- Base units and derived units are different sets. Follow any symbol-length restriction in the question; adding a metric prefix does not create another base unit.
These notes explain the question boundary; they are not a ranking of player mistakes.
Why these answers qualify
Each entry belongs to the bounded set defined by the prompt. The named source supports the underlying facts; our editorial scoring is a separate layer.
Source: BIPM · SI base units and quantities ↗
Reference version: 2026-10-02. See our answer policy for how we handle aliases and omissions.