What is the complementary color of red?

Which of the following colors are primary colors?

What kind of lens is used in the spectacles of a person suffering from myopia (near-sightedness)?

$(i)$ Calculate the maximum power of accommodation of a person having normal vision.
$(ii)$ $A$ person needs to use glasses for reading a newspaper. Identify the defect in her vision and the type of lens she would need to correct it.
$(iii)$ Sometimes when we enter a dark room from bright sunlight,we are unable to see objects clearly. Why?

Why does the sky appear dark and black to an astronaut instead of blue?

When white light is incident on a yellow pigment,which color of light is not reflected?