Which metal is stored in kerosene?

Generally,when metals are treated with mineral acids,hydrogen gas is liberated,but when metals (except $Mn$ and $Mg$) are treated with $HNO_3$,hydrogen is not liberated. Why?

State whether the following statement is true or false:
Iron does not burn on heating,but iron filings burn vigorously when sprinkled in the flame of a burner.

Generally, metals react with acids to produce salt and hydrogen gas. Which of the following acids does not produce hydrogen gas when reacting with most metals (except $Mn$ and $Mg$)?

How will you test for the gas which is liberated when hydrochloric acid reacts with an active metal?

Why does a magnesium ribbon start floating when it is placed in hot water?