What type of oxide is phosphorus pentoxide $(P_4O_{10})$?

Solder is an alloy of lead and tin. It has a:

Which of the following elements will form an acidic oxide?

Explain why calcium metal starts floating on the surface of water after reacting with it. Write the chemical equation for the reaction.

Explain the following statements:
$(a)$ Most metal oxides are insoluble in water but some of these dissolve in water. What are these oxides and their solutions in water called?
$(b)$ At ordinary temperature,the surfaces of metals such as magnesium,aluminium,and zinc are covered with a thin layer. What is the composition of this layer? State its importance.
$(c)$ Some alkali metals can be cut with a knife.

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.