$A$ metal $(A)$ on heating in nitrogen gas gives compound $(B)$. $(B)$ on treatment with $H_{2}O$ gives a colourless gas which when passed through $CuSO_{4}$ solution gives a dark blue-violet coloured solution. $(A)$ and $(B)$ respectively,are

The main oxides formed on combustion of $Li, Na$ and $K$ in excess of air are,respectively:

The order of negative standard electrode potential values $(E^\circ_{M^+/M})$ for $Li$,$Na$,and $K$ is:

Which property of sodium is being used in street lights?

The metal which reacts with water at room temperature is

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 :