In the following compounds, the favourable site|s for protonation is |are.

In the following compounds, the favourable site/s for protonation is /are.
In the following compounds, the favourable site|s for protonation is |are.
In the following compounds, the favourable site|s for protonation is |are.
In the following compounds, the favourable site|s for protonation is |are.

/are.