The compound formed on heating sodium metal in a current of dry ammonia gas is

Which of the following is the correct arrangement in increasing order of solubility?

Which of the nitrates on strong heating leaves the metal as the residue?

Sodium is produced by the electrolysis of a molten mixture of about $40\%$ $NaCl$ and $60\%$ $CaCl_2$ because

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 ......

From which of the following minerals is $Ra$ (Radium) obtained?