Which of the following compounds would decrease the pH of solution?

• A. SrBr₂
• B. KSH
• C. NaN₃
• D. NiP
• E. Hg₂Cl₂

Answer: (D)

Verified step by step guidance

1. Identify the nature of each compound by considering the ions they produce in aqueous solution and whether those ions are acidic, basic, or neutral.
2. For SrBr\_2, recognize that Sr\^{2+} is a metal cation from a strong base (Sr(OH)\_2) and Br\^- is the conjugate base of a strong acid (HBr), so SrBr\_2 will produce a neutral solution and not affect pH significantly.
3. For KSH, note that K\^+ is a neutral cation (from strong base KOH), but SH\^- (hydrosulfide ion) is the conjugate base of a weak acid (H\_2S), so it can act as a weak base and increase pH.
4. For NaN\_3, Na\^+ is neutral, and N\_3\^- (azide ion) is the conjugate base of a very weak acid (HN\_3), so it tends to make the solution slightly basic or neutral.
5. For NiP, consider that Ni is a transition metal cation that can hydrolyze in water to produce H\^+ ions, making the solution acidic and thus decreasing the pH.