What is the molecular formula of phosphorus pentoxide?

State whether the following statement is true or false:
At ordinary temperature,the surfaces of metals such as magnesium,aluminium,zinc,lead,etc.,are covered with a thin layer of oxide which prevents the metal from further oxidation.

Name one metal and one non-metal that exist in liquid state at room temperature. Also,name two metals having a melting point less than $310\ K$ $(37\ ^\circ C)$.

$(a)$ Write the chemical name of the coating that forms on silver and copper articles when these are left exposed to moist air.
$(b)$ Explain what is galvanisation? What purpose is served by it?
$(c)$ Define an alloy. How are alloys prepared? How do the properties of iron change when:
$(i)$ small quantity of carbon,
$(ii)$ nickel and chromium are mixed with it.

$(i)$ Arrange the following metals in the order of their decreasing activities: Aluminium, Gold, Sodium, Copper.
$(ii)$ Give the reaction of aluminium powder with manganese dioxide on heating.

$A$ metal $M$ does not liberate hydrogen from acids but reacts with oxygen to give a black coloured product. Identify $M$ and the black coloured product,and also explain the reaction of $M$ with oxygen.