Answer:
Option D is Correct
frequent venting through the stopcock is necessary to prevent pressure buildup
Explanation:
To use a separatory funnel, the two phases and the mixture to be separated in solution are added through the top with the stopcock at the bottom closed. The funnel is then closed and shaken gently by inverting the funnel multiple times; if the two solutions are mixed together too vigorously emulsions will form.
To avoid pressure build up it is essential that the stopcock be opened frequently.
CAUTION: Be careful where you point the stem of the funnel because liquid can be blown out.