Which of the following metals is not found in the free state?

What is the chemical formula of washing soda?

Given below are two statements: One is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A$ :- Sodium is about $30$ times as abundant as potassium in the oceans.
Reason $R$ :- Potassium is bigger in size than sodium.
In the light of the above statements,choose the correct answer from the options given below:

The $Cs^{+}$ ion imparts a violet color to the flame. This is due to the fact that the emitted radiation has .........

The blue color of a solution of sodium in liquid ammonia is due to:

Hydrogen,by donating one electron,forms $H^+$. In this property,it resembles