Lithium nitrate on heating gives

Given below are two statements: one is labelled as Assertion $A$ and the other is labelled as Reason $R:$
Assertion $A:$ Metallic sodium dissolves in liquid ammonia giving a deep blue solution,which is paramagnetic.
Reason $R:$ The deep blue solution is due to the formation of amide.
In the light of the above statements,choose the correct answer from the options given below:

What is caused by an excess of $Na^+$ in the human body?

Which of the following is the most important biological compound containing $Mg$ found in the living world?

$A$ metal $M$ reacts with $N_2$ to form a compound $A$ $(M_3N)$. Heating $A$ at high temperature gives back $M$,and passing $A$ through $H_2O$ produces gas $B$. Gas $B$ turns $CuSO_4$ solution into a deep blue color. What are $A$ and $B$?

Which of the following is the reason why sodium metal conducts electricity?