UPSC Civil Services Model Paper 4

The Vertical-horizontal illusion is the tendency for observers to overestimate the length of a vertical line relative to a horizontal line of the same length.
Bezold effect is an apparent change of tone of a colour due to the alteration of the colour of the background.
The autokinetic effect, or autokinesis, occurs when a stationary image appears to move.
The scattering of light (also known as the Tyndall effect) causes these illusions (blue sky, red sunset/sunrise).
So, options 2, 3, and 4 are NOT correct.