What is the number of electrons lost by a metal atom to form a positive ion called?

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.

In the refining of silver,the recovery of silver from silver nitrate solution involves displacement by copper metal. Write down the reaction involved.

Which of the following metals is the most reactive?

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

Which of the following pairs will give displacement reactions?