does it form any volcanic arc?
Yes, the Campanian volcanic arc.
Mount Vesuvius
The volcano is one of several which form the Campanian volcanic arc. 
how many times has mount vesuvius erupted since 79 ad It has erupted many times since, and is the only volcano on the European mainland to have erupted within the last hundred years. where is it located? It located on the Gulf of Naples in Campania, Italy. when did it first erupt? AD 79 which are the cities that are living near enough to be affected by an eruption? Avellino, Salerno and Naples are some of them. how is its appearance described? It is a "humpbacked" peak, consisting of a large cone partially encircled by the steep rim of a summit caldera caused by the collapse of Mount Somma. where is the last mentioned mountain located? It is located in the Province of Naples, in the Campania region of southern Italy. the volcanic mountain mentioned in the beginning is it still regarded as an active volcano? Yes how did this mountain form? It was formed as a result of the collision of two tectonic plates, the African and the Eurasian.
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Mount Vesuvius [SEP] Formation
Others include Campi Flegrei, a large caldera a few kilometers to the north west, Mount Epomeo, to the west on the island of Ischia, and several undersea volcanoes to the south. The arc forms the southern end of a larger chain of volcanoes produced by the subduction process described above, which extends northwest along the length of Italy as far as Monte Amiata in Southern Tuscany. Vesuvius is the only one to have erupted within recent history, although some of the others have erupted within the last few hundred years. Many are either extinct or have not erupted for tens of thousands of years.