Answer to Question 1
Answer: Water is a strong absorber of infrared radiation because its molecules resonate to the frequencies of infrared light. Water also absorbs visible red light, but not so much. So water is weak in reflecting red light (it can't absorb and reflect the same light). To say it weakly reflects red light is to say it strongly reflects the complementary color of red, which is cyan (greenish blue).
Answer to Question 2
Answer: Nitrogen and oxygen molecules in the atmosphere scatter light of high frequencies more than light of low frequencies. When sunlight encounters the atmosphere, light is scattered by molecules that make up the atmosphere. Violet and blue light are scattered the most by atmospheric molecules, and because our range of vision better sees blue than violet, the sky looks blue to us.
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