"Water is an important for our lives." This is not a correct sentence. I can understand why "an" puzzles you. "Water is important for our lives." This is correct.
"sun" is not a proper noun. It does not start with a capital letter.
The sun is shining. Correct. The Sun is shining. Not correct.
Hi, hanuman IMPORTANT is adjective, when you use AN before it, you need a noun after it. ''Water is an important for our lives.'' Incorrect Water is an important element in our lives. OK Water is important for us. OK As you said, water is uncountable noun and it isn't correct to use A before it. I need some water. This water is very clean. When it comes to
This is incorrect. As you can see, important is an adjective. So you have to rewrite the sentence as "Water is important in our lives." or "Water plays an important role in our daily life."
This is a perfect sentence. The sun rises in the east and sets in the west.