Vinegar has a pH of 3, and household ammonia has a pH of 11. Is the concentration of H + greatest in the vinegar or ammonia?

In vinegar of course, which is an acid.

pH=3=-log10^-3 [H3O+]1=10^-3M

Also, for NH3: pH=11 [H3O+]2=10^-11M<[H3O+]1

But you should tell your teacher that the correct way to compare these two is by Ka, so you need more information.

Vinegar.

Explanation:

pH is the negative logarithm of the hydrogen ion concentration. pH scale has the values to measure the acidity and basicity of the substance.

Acids may be defined as the substance that pH less than seven and base the substance of pH more than seven. Since, vinegar has pH 3 it is acidic in nature and contains more H+ions then ammonia because ammonia is basic in nature.

Thus, the answer is vinegar.