Which of the following methods is suitable for preventing an iron frying pan from rusting ?

Samples of four metals $A$, $B$, $C$ and $D$ were taken and added to the following solution one by one. The results obtained have been tabulated as follows.

Use the Table above to answer the following questions about metals  $A$, $B$, $C$ and $D$.

$(i)$ Which is the most reactive metal ?

$(ii)$ What would you observe if $B$ is added to a solution of Copper $(II)$ sulphate ?

$(iii)$ Arrange the metals $A$, $B$, $C$ and $D$ in the order of decreasing reactivity.

Which gas is produced when dilute hydrochloric acid is added to a reactive metal? Write the chemical reaction when iron reacts with dilute $H_2SO_4$.

Give reasons : Sodium, potassium and lithium are stored under oil.

Pratyush took sulphur powder on a spatula and heated it. He collected the gas evolved by inverting a test tube over it, as shown in figure below.

$(a)$ What will be the action of gas on

$(i)$ dry litmus paper ?

$(ii)$ moist litmus paper ?

$(b)$ Write a balanced chemical equation for the reaction taking place.