Why danger signals are red

The same question, asked 3 times: 2023*, 2025*, 2026. Every wording below, oldest first.

Try each one first, then open its answer.

Question 1
2023
31 $Give reasons for the following : (a) Danger signals installed at airports and at the top of tall buildings are of red colour. (b) The sky appears dark to the passengers flying at very high altitudes. (c) The path of a beam of light passing through a colloidal solution is visible.$
Question 2
2025
25 (a) $Give reasons : (i) The sky appears dark to passengers flying at very high altitude. (ii) ‘Danger’ signal lights are red in colour.$
Question 3
2026
37 $(a) What is Tyndall effect ? (b) What happens when sunlight is scattered from the particles of very large size ? (c) ‘Danger’ signals are always red in colour. Why ?$

Question 1