Which of the following metals displaces $SO_2$ gas from concentrated sulphuric acid?

Oxygen gas can be prepared from solid $KMnO_4$ by

When magnesium burns in air,the compounds of magnesium formed are magnesium oxide and

Which of the following methods is generally used for the extraction of alkali metals?

Chemically,philosopher's wool is

Fill in the blanks:
$(1)$ Sodium hydroxide is also known as ......
$(2)$ The reaction of sodium amalgam with water produces ...... and ...... gas.
$(3)$ Sodium hydroxide on reaction with $CO_2$ produces ......
$(4)$ Sodium hydrogen carbonate is known as ......