pH reflects [H+] concentration for strong acids

Steps:

• pH = -log[H+]; pH 2 (HNO3) gives [H+] ≈ 0.01 M, pH 4 (HCl) gives [H+] ≈ 0.0001 M.
• HCl and HNO3 are both strong acids, fully dissociating to produce H+.
• For strong acids, [H+] equals initial acid concentration, assuming dilute solutions.
• Higher [H+] in HNO3 indicates greater concentration than in HCl.

Why C is correct:

• pH inversely relates to [H+] via pH = -log[H+]; for strong acids, lower pH directly means higher concentration.

Why the others are wrong:

• A: Both HCl and HNO3 are strong acids, not weak.
• B: Lower pH of HNO3 shows greater acidity than HCl.
• D: Both strong acids fully dissociate; dissociation extent is equal, not more for HCl.

Final answer: C