Dolomite is an ore of which metal?

Although metals form basic oxides,which of the following metals form an amphoteric oxide?

The following reaction takes place when aluminium powder is heated with $MnO_2$:
$3MnO_2(s) + 4Al(s) \rightarrow 3Mn(l) + 2Al_2O_3(l) + \text{Heat}$
$(a)$ Is aluminium getting reduced?
$(b)$ Is $MnO_2$ getting oxidised?

$(a)$ When calcium metal is added to water,the gas evolved does not catch fire,but the same gas evolved on adding potassium metal to water catches fire. Explain why?
$(b)$ Name a metal for each case:
$(i)$ It displaces hydrogen gas from nitric acid.
$(ii)$ It does not react with any physical state of water.
$(iii)$ It does not react with cold as well as hot water but reacts with steam.

Which of the following gases is insoluble in water?

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 $310\ K$ $(37\ ^\circ C)$.