Which of the following when added to 20 mL of a 0.01 M solution of HCl would decrease its pH ?

Step-by-step solution

For an acid, pH of an acid solution will be lower as the solution is more concentrated. pH =- [ H ⁺ ] aligned & M _ a = M ₁ ~V ₁+ M ₂ ~V ₂ ~V ₁+ V ₂ &= 2 10⁻² 10⁻²+2 10⁻² 2 10⁻² 4 10⁻² =1.5 10⁻² & M _ b = 2 10⁻² 10⁻²+2 10⁻² 5 10⁻³ 4 10⁻² =0.75 10⁻² & M _ c = 2 10⁻² 10⁻²+2 10⁻² 1 10⁻² 4 10⁻² & M _ c =1 10⁻² & M _ d = 2 10⁻² 10⁻²+4 10⁻² 5 10⁻³ 6 10⁻² &= 4 10⁻⁴ 6 10⁻² & M _ d =0.66 10⁻² aligned Order of concentration : M_a M_c M_b M_d Order of pH :- M _ d M _ b M _ c M _ a M _ a have the lowest pH.