An aqueous solution of HCl has a pH of 2.0 When water is added to increase the pH to 5.0 the hydrogen ion concentration -

Options

A. remains the same
B. decrease three-fold
C. increases three-fold
D. decreases thousand-fold

Answer

D

Explanation

`pH=2 rArr [H^(+)]=10^(-2)`
`pH=5 rArr [H^(+)]=10^(-5)`
`:. ([H^(+)]"new")/([H^(+)]"old")=(10^(-5))/(10^(-2))=10^(-3)`