$Cs^{+}$ ions impart violet colour to Bunsen flame. This is due to the fact that the emitted radiations are of

Which of the following metals is the most reactive?

Which one of the following alkali metals gives hydrated salts?

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:

Consider the following reactions:
$Cs + O_2 \text{ (excess)} \rightarrow X$
$Na + O_2 \rightarrow Y$
Identify the correct statement about $X$ and $Y$.

What is the gas produced in the reaction: $KO_2 + CO_2 \to ?$