Name two metals which react with dilute $HNO_{3}$ to evolve $H_{2}$ gas.

What happens when calcium is treated with water?

Which metal does not react even with hot water or steam?

Which of the following is not a use of sulfur?

$(a)$ 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 process is used to convert sulphide ores into oxides by heating them in the presence of excess air?