The pH of a 0.001 M HCl solution is ___________
The pH of an acidic solution can be calculated using the formula: \[ pH = -\log [H^+] \] Given a hydrochloric acid (HCl) concentration of 0.001 M: \[ pH = -\log \left( 1 \times 10^{-3} \right) = 3 \] Hence, the correct answer is (C) 3.