The correct answer is option 1: red light is least scattered by the atmosphere.

When the Sun is near the horizon, its light has to pass through a larger portion of Earth`s atmosphere compared to when it is directly overhead. The Earth`s atmosphere is made up of molecules and particles that interact with light. When light from the Sun enters the atmosphere, it undergoes a process called scattering, where it interacts with these particles and changes direction.

The scattering of sunlight depends on the wavelength or color of light. Shorter wavelength light, such as blue and violet, tends to scatter more easily, while longer wavelength light, such as red and orange, scatters less. This is known as Rayleigh scattering.

Because blue and violet light scatter more easily, they are more likely to be scattered out of our line of sight as the Sun`s light passes through the atmosphere. This leaves predominantly red and orange light to reach our eyes, giving the Sun a reddish appearance.

So, when the Sun is near the horizon, the longer wavelength red light is least scattered by the atmosphere, resulting in the observed reddish color. Option 1 correctly explains this phenomenon.