Calculate the pH values of the following solutions: 

a) 1.00x10^-2 M selenic acid (H₂SeO₃) solution. (Ka₁ = 3.0x10^-3 , Ka₂ = 5.0x10^-8 )

b) 100.00 mL 0.100 M arsenic acid (H₃AsO₄) and 100.00 mL 0.100 M sodium hydroxide Solution containing (NaOH). (Ka₁ = 5.5x10^-3 ; Ka₂ = 1.7x10^-7 )

c) 20.00 mL 0.0600 M nitrous acid (HNO₂) solution, 30.00 mL 0.0400 M sodium nitrite The solution formed when mixed with (NaNO₂) solution. (Ka = 5.6x10^-4 )

d) A solution containing 0.0100 M HClO₄ and 0.0300 M CH₃COOH (Ka = 1.7x10^-5 )