BPSC 69th CCE Prelims General Studies · Question 40 of 144

Correct — A, a-2, b-3, c-4, d-1. Two of the four pairings are settled by colour theory and carry the whole question. In the additive (RGB) model used by every screen, the three primaries of light are red, green and blue, and mixing them in pairs gives the three secondaries: red and green give yellow, green and blue give cyan, red and blue give magenta. Magenta sits exactly midway between red and blue on the colour wheel and is the complement of green — mix magenta light with green light and you get white. So magenta must take item 2, 'Red and blue', and cyan must take item 1, 'Green and blue'. Yellow, the third secondary, has been left out of the list precisely so that these two cannot be confused with it. Those two pairings alone eliminate options (c) and (d), and the two that survive, (a) and (b), already agree on them — so the entire question reduces to whether teal takes item 3 and mauve item 4, or the other way round. One word decides it. Item 3 contains green and item 4 contains red. Teal is a dark cyan, named after the blue-green stripe on the head of the Eurasian teal duck (Anas crecca), so it belongs to the green side and takes item 3. Mauve is a pale purple, named after the mallow flower, sitting on the red-blue axis with no green in it at all, so it takes item 4 — and 'Blue, red and white' is in fact a textbook description of mauve, since a pale purple is exactly a red-blue mix lightened. That gives magenta 2, teal 3, mauve 4, cyan 1, which is the sequence 2, 3, 4, 1 — option (a).

• (b)a b c d 2 4 3 1 — This is the only serious rival and the reason the question is worth attempting rather than guessing. It gets both certainties right — magenta as red and blue, cyan as green and blue — and then swaps the remaining two, making teal 'Blue, red and white' and mauve 'Blue, green and white'. Both halves of that swap are wrong in the same way: teal is a blue-green and cannot be described without green, while mauve is a pale purple and contains no green at all. If you can only remember one thing here, remember that teal is the green one.
• (c)a b c d 4 2 1 3 — This makes magenta 'Blue, red and white' and cyan 'Blue, green and white' — that is, it turns both of the fully saturated secondary colours into pale tints. Magenta and cyan are produced by two primaries at full intensity, with no white added; the moment white is mixed in you have moved to pink or to a pale sky blue. It also gives teal 'Red and blue', which has no green in it, so this option fails on three of its four pairings.
• (d)a b c d 3 4 2 1 — This pairs magenta with 'Blue, green and white', which is the one combination magenta can never be: green is magenta's complementary colour, the colour it is defined against, and magenta light plus green light gives white. It then gives teal 'Blue, red and white', again removing the green from a blue-green. Only its cyan pairing survives, and one right pairing out of four is not enough to rescue the code.

Colour mixing follows two different rule sets and most confusion comes from mixing them up. Additive mixing applies to light: the primaries are red, green and blue, pairs of them make the secondaries yellow, cyan and magenta, and all three together make white. This is how screens work, because a display emits light. Subtractive mixing applies to inks and pigments, which work by absorbing light rather than emitting it: here the primaries are cyan, magenta and yellow, pairs of them make red, green and blue, and all three together make a muddy near-black, which is why printers add a fourth ink, black or 'key', giving CMYK. The two systems are mirror images — each additive secondary is a subtractive primary, and vice versa. On top of the hue itself sit three modifications that explain the rest of the list: adding white to a hue gives a tint, adding black gives a shade, and adding grey gives a tone. Mauve is a tint of the red-blue region — a pale purple. Teal is a shade of cyan — cyan mixed with black or grey. That is the vocabulary the question is testing through the back door. Two further points make the system stick. First, the reason there are three primaries at all is physiological: the human retina carries three kinds of cone cell, sensitive to long, medium and short wavelengths, so any colour we can see can be reproduced by feeding those three receptors in the right proportion — colour television and computer displays are built directly on that fact. Second, the names of these colours are historical accidents rather than technical coinages: magenta and mauve are both nineteenth-century aniline dyes, teal is a duck, and cyan comes from the Greek kyanos for a dark blue. Knowing where a colour name comes from is often the fastest way to remember which family it belongs to, which is exactly the trick this question rewards.

Attack this as a two-certainties-then-one-word problem rather than as four independent recalls, which is the general method for any match-the-list item. First pin what you are sure of: magenta is red plus blue and cyan is green plus blue, and both surviving options agree, so those pairings buy you the elimination of (c) and (d) and nothing more. Then find the single word that separates the last two items. Items 3 and 4 differ only in green versus red, so the question becomes: does teal contain green, or does mauve? Teal is a blue-green — the word names a duck with a blue-green head stripe — and mauve is a pale purple named after the mallow flower. Green goes with teal. Two honest cautions belong here. The first is that this is a match-list item with no anchor outside general knowledge, so it is finely balanced in a way a factual question is not: the reasoning above is what carries the answer, not a published authority. The second is that item 3's description is loose. Teal is standardly made by darkening cyan with black or grey, not by adding white to a blue-green, so 'Blue, green and white' is an approximation; item 4, by contrast, describes mauve accurately. But since both readings agree that green belongs with teal and red with mauve, the looseness does not change the answer.

• Additive (RGB) mixing of light: red + green = yellow, green + blue = cyan, red + blue = magenta, and all three together = white; this is the model that fixes two of the four pairings in this question.
• Subtractive (CMY) mixing of inks reverses it: cyan + magenta = blue, cyan + yellow = green, magenta + yellow = red, and all three give a muddy near-black, which is why printing adds a fourth 'key' black ink to make CMYK.
• Magenta lies midway between red and blue on the colour wheel and is the complementary colour of green — magenta light plus green light gives white — which is why no combination containing green can describe it.
• Teal is a dark cyan, created by mixing cyan with black or grey, and is named after the Eurasian teal (Anas crecca), whose head carries a blue-green stripe; the flag of Sri Lanka uses teal.
• Mauve is a pale purple named after the mallow flower, containing more grey and blue than a pale tint of magenta and often described as pale violet — a red-blue mix lightened, exactly as item 4 puts it.
• Terminology that decides such questions: a hue plus white is a tint, a hue plus black is a shade, a hue plus grey is a tone — mauve is a tint, teal a shade.
• Mauve has a place in the history of chemistry: mauveine, the first aniline dye and one of the first synthetic dyes ever mass-produced, was discovered by chance in 1856 by the eighteen-year-old William Henry Perkin while he was trying to synthesise quinine for malaria; the colour took the name mauve in 1859.
• Magenta is named after a battle. The aniline dye was patented in 1859 by the French chemist François-Emmanuel Verguin as fuchsine, and was renamed to mark the French-Sardinian victory over Austria at the Battle of Magenta in Lombardy on 4 June 1859, during the Second Italian War of Independence.

• Applying the printing rule inside the light rule — in subtractive mixing cyan and magenta give blue, but in additive mixing red and blue give magenta; both are correct in their own system
• Treating teal as a kind of purple: it is a dark cyan, a blue-green, and the green is what separates it from mauve
• Trying to recall all four pairings at once instead of locking the two certain ones first and then deciding the remaining pair on a single word

BPSC puts general-science material into a match-the-list frame and lets the code options do the work, so a candidate who is sure of only two pairings can still reach the answer by elimination — which is exactly how this one is designed to be solved. UPSC asks the same colour material more directly and more technically: it has asked what process the term CMYK belongs to, and it has asked, in a statement format, what colour results when magenta and yellow or cyan and magenta overlap, where the subtractive rule has to be applied correctly rather than remembered as a list.

• practice — not a real PYQ

  In additive colour mixing, which colour is produced when red light and green light are combined?

  • (a)Cyan
  • (b)Magenta
  • (c)Yellow
  • (d)White

  Answer(c) Yellow — red, green and blue are the additive primaries, and their pairs give yellow (red + green), cyan (green + blue) and magenta (red + blue).

• practice — not a real PYQ

  Adding white to a hue produces a ______, while adding black to the same hue produces a ______.

  • (a)tint; shade
  • (b)shade; tint
  • (c)tone; tint
  • (d)shade; tone

  Answer(a) tint; shade — mauve is a tint of the red-blue region, while teal is a shade of cyan, made by mixing cyan with black or grey.