Question:

Sentences given in each question, when properly sequenced, form a coherent paragraph. The first and last sentences are 1 and 6, and the four in between are labelled A, B, C and D. Choose the most logical order of these four sentences from among the four given choices to construct a coherent paragraph from sentences 1 to 6.

1. Security inks exploit the same principle that causes the vivid and constantly changing colours of a film of oil on water.

A. When two rays of light meet each other after being reflected from these different surfaces, they have each travelled slightly different distances.

B. The key is that the light is bouncing off two surfaces, that of the oil and that of the water layer below it.

C. The distance the two rays travel determines which wavelengths, and hence colours, interfere constructively and look bright.

D. Because light is an electromagnetic wave, the peaks and troughs of each ray then interfere either constructively, to appear bright, or destructively, to appear dim.

6. Since the distance the rays travel changes with the angle as you look at the surface, different colours look bright from different viewing angles.

Show Hint

Look for the sentence that names the two surfaces first, since "these different surfaces" in another sentence needs an antecedent.
Updated On: Nov 4, 2026
  • ABCD
  • BDAC
  • BADC
  • DCAB
Show Solution
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The Correct Option is C

Solution and Explanation

Step 1: Find the opening link:
Sentence 1 introduces the oil film. Sentence B explains the key idea: light bounces off two surfaces (oil and water). It must come first, because A speaks of "these different surfaces", which refers back to B.

Step 2: Place A and D:
A says two rays meet after reflection and have travelled different distances. D then says the peaks and troughs "of each ray" interfere "then" - the word "then" follows the meeting of the rays in A. So A comes before D.

Step 3: Place C:
C says the distance the two rays travel decides which colours look bright. It follows the interference described in D, and leads to sentence 6, which says the distance changes with viewing angle.

The order is B, A, D, C.

Step 4: Check the options:
(1) ABCD starts with "these different surfaces" with no antecedent. (2) BDAC puts interference of "each ray" before the rays meet. (4) DCAB begins with "Because light is an electromagnetic wave" with no earlier mention of rays.

Final Answer:
The correct option is (3): BADC
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