During sunrise/sunset, the looks reddish. This is because at this because at this stage, rays from the sun have to travel a much larger part of atmosphere. The red colour having largest wavelength is scattered the least.
At noon, the sun is nearly overhead. The sunlight has to pass through much smaller portion of earth's atmosphere the scattering is much less and the sun looks white.

When sunlight passes through the atmosphere, most of the light having longer wavelengths do not get scattered much. But the light of shorter wavelength scattered all around the sky by air molecules present in the atmosphere. Some of this scattered blue light enters our eyes and so in whichever direction we look, the sky looks blue.
Thus, we can say that the sky appears blue due to the molecules in air which scatter the blue part of the sunlight much more easily than the red light or other shades.

No, what is seen by us is not the true position of the star. Infact, starts seem higher than they actually are on account of atmospheric refraction.

Human eye can see clearly the nearby object as well as the distant objects by changing the focal length/power of accommodation of the human eye.

No, a person may have normal of accommodation and yet he may be myopic or hypermetropic. Infact. Myopia may arise when length of eye ball elongated and hypermetropia may arise when length of eye ball gets shortened.

Planets are very close to the earth as compared to the stars. They also act as extended source of light. The total variation in the amount of light entering our eyes from all the individual point sized sources will average out to zero, which nullify the twinkling effect of each other. So, planets do not twinkle.

The image distance remains the same because the focal length of the eye lens gradually changes to maintain the position of image on the retina of the eye.

As our eye cannot focus the objects placed closer than 25 cm on the retina. we are unable to see the objects clearly.

For correcting myopia, concave lens is required.
The image of a distant object should be formed at 80 cm by the concave lens.
\(\therefore\) u = -\(\infty\), v = -80 cm
By lens formula, \(\begin{aligned} \frac{1}{f} & =\frac{1}{v}-\frac{1}{u} \\ \end{aligned}\)
\(\begin{aligned} & =\frac{1}{-80}-\frac{1}{\infty}=\frac{-1}{80} \end{aligned}\)
\(\text { Power }=\frac{1}{f(\text { in metre })}=\frac{-100}{80}\)
= - 1.25D