Final answer:
The negation of the statement "The sky is blue" is b) "The sky is not blue." This is the direct opposite of the original statement, asserting that the sky lacks the color blue.
Step-by-step explanation:
The negation of a statement simply means stating the opposite of what the original statement claims. In the case where the original statement is "The sky is blue," the correct negation of this statement would be "The sky is not blue." This means that the correct answer is b) The sky is not blue. Adding 'not' to a statement is the most straightforward way to negate it. Therefore, options a), c), and d) are incorrect as they suggest specific alternative colors which do not serve as a direct negation of the original statement.