Answer:
The correct approach is "3.1×10⁻³ M".
Explanation:
As we know,
[tex]pH=-log[H_{3}O^+][/tex]
[tex]pH=2.5[/tex]
[tex][H_{3}O]^+= \ ?[/tex]
Now,
⇒ [tex]-log[H_{3}O]^+=2.5[/tex]
⇒ [tex][H_{3}O]^+=10^{-2.5}[/tex]
⇒ [tex]=3.1\times 10^{-3} \ M[/tex]
So that the needed molar concentration of HCL will be:
= [tex]3.1\times 10^{-3} \ M[/tex]
