Which one of the following is not the function of vagus nerve?

The 9^th and 10^th cranial nerves have their origins similar, i.e. side of medulla oblongata, but are distributed in different areas, hence have different functions. They actually control the voluntary and involuntary movements of pharynx, larynx and many visceral organs.

Saliva secretion is not the function of vagus. Vagus is the 10^th cranial nerve, which is branched and the longest of all cranial nerves. It is mainly responsible for swallowing, phonation, intestinal and gastric movement, general taste, gastric and pancreatic sensation, breathing and cutaneous sensibility. Saliva secretion from the salivary gland is the function of 9^th cranial nerve namely glossopharyngeal nerve. This nerve is also responsible for larynx elevation and taste sensation of posterior tongue.