Step 1: Use the scale:
pH 7 is neutral, below 7 is acidic and above 7 is basic. Blood is mildly alkaline.
Step 2: Pick the value:
Medical references give arterial blood pH as 7.35 to 7.45, centred at 7.4. Only option C lies in this range.
Step 3: Check the rest:
Options A and B are at or below neutral and D is above 8, which the body cannot tolerate.
Final Answer:
Blood is slightly basic with a normal pH of 7.4.
\[ \boxed{\text{(C) }7.4} \]