SOLUTION
From the question, we have been given the equation for pH and we want to calculate the concentration of hydrogen given as H+
This becomes
[tex]\begin{gathered} pH=−logH^+ \\ \end{gathered}[/tex]We were given the pH as 4. Substituting this into the equation, we have
[tex]\begin{gathered} 4=-logH^+ \\ -logH^+=4 \\ logH^+=-4 \\ taking\text{ antilog, we have } \\ antilog(logH^+)=antilog-\text{ 4} \\ H^+=0.0001 \end{gathered}[/tex]Hence the answer is 0.0001 the last option