Correct order of density is

Which of the following statements is correct regarding alkali metals?

Given below are two statements:
Statement $I$ : The $4f$ and $5f$-series of elements are placed separately in the Periodic table to preserve the principle of classification.
Statement $II$ : $S$-block elements can be found in pure form in nature.
In the light of the above statements,choose the most appropriate answer from the options given below :

Give two uses of $KOH$.

Nitrogen dioxide $(NO_2)$ cannot be obtained from the thermal decomposition of which of the following?

Lithium nitrate on heating gives