Step 1: Approach
Compare with the pH table for strong acids: pH is the power of ten of $[\text{H}^+]$ with its sign changed.
Step 2: Write $[\text{H}^+]$ as a power of ten
Complete dissociation gives $[\text{H}^+] = 1\ \text{M} = 10^{0}\ \text{M}$.
Step 3: Read off the pH
The exponent is $0$, so $\text{pH} = 0$.
Step 4: Cross-check
For 0.1 M the exponent is $-1$ and pH is 1; for 0.01 M the pH is 2. Our solution is ten times stronger than 0.1 M, so its pH is one unit lower than 1, which is 0. That is option (C).
Final Answer:
The pH of 1 M HCl is 0, option (C).
\[ \boxed{0} \]