Identify the components present

The solution contains:

• $1\,\text{M } \mathrm{NaCl}$
• $1\,\text{M } \mathrm{HCl}$

Check whether it can be a buffer

A buffer solution requires:

• a weak acid and its conjugate base, or
• a weak base and its conjugate acid.

Here:

• $\mathrm{HCl}$ is a strong acid
• $\mathrm{NaCl}$ is a salt of a strong acid ($\mathrm{HCl}$) and a strong base ($\mathrm{NaOH}$)

Since neither a weak acid/base nor its conjugate pair is present, this solution cannot act as a buffer.

Determine the pH nature of the solution

$\mathrm{HCl}$ is a strong acid and dissociates completely: $\mathrm{HCl} \rightarrow \mathrm{H^+} + \mathrm{Cl^-}$

Since the concentration of $\mathrm{HCl}$ is $1\,\text{M}$, $[\mathrm{H^+}] \approx 1\,\text{M}$

Therefore, $\mathrm{pH} = -\log(1) = 0$

So the solution has: $\mathrm{pH} < 7$

Evaluate the options

• A: not a buffer solution with $\mathrm{pH}<7$ ✅
• B: not a buffer solution with $\mathrm{pH}>7$ ❌
• C: a buffer solution with $\mathrm{pH}<7$ ❌
• D: a buffer solution with $\mathrm{pH}>7$ ❌

Final answer

The solution is not a buffer and is acidic.

Hence, the correct option is A.