Q1.
Day and night cycle, seasons, the life on the Earth... so much is dependent upon the Sun. Could the light from the Sun get blocked by the two planets which are revolving between the Earth and the Sun?
Answer
No. The two planets that revolve between the Earth and the Sun are Mercury and Venus, and neither of them can ever block the Sun's light from reaching us.
They are much larger than the Moon, but they are also enormously farther away, so their apparent size in the sky is tiny compared with the Sun's. When Venus does pass between the Sun and the Earth it shows up only as a small black dot creeping across the bright face of the Sun — the rare event called the Transit of Venus.
The Moon, however, can do it. It is far smaller than the Sun in actual size, but it is so much closer to us that its apparent size in our sky is about the same as the Sun's. That is why the Moon can cover the Sun completely and cause a solar eclipse.
Why it happens: apparent size depends on actual size and distance. Doubling the distance halves the apparent size. Venus is roughly 100 times farther from us than the Moon, so even though it is bigger than the Moon it looks like a dot.
Did you know? A Transit of Venus is rarer than a solar eclipse. The last pair occurred in 2004 and 2012; the next will not be until 2117.