Answer:
b) By mixing weak base with its conjugate acid and then adjusting the pH with strong acid.
Explanation:
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In this case, considering that the buffer required a pH greater than 7 where the basic conditions are present, we need a weak base and its conjugate base in order to assure such pH greater than 7. Moreover, by using a strong acid, we can gently add it in order to decrease the pH up to 7.4 via a properly measured neutralization of the necessary moles of base up to a hydrogen concentration of 3.98x10⁻⁸ (pH). Therefore, answer is b) By mixing weak base with its conjugate acid and then adjusting the pH with strong acid.
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I say the answer to your question is False because Day and Night are caused by the rotation on its axis!
I believe that D is the answer to your question, even though this is a complicated one.