Which of the following elements exhibits the highest photoelectric effect?

On combustion of $Li$,$Na$,and $K$ in excess of air,the major oxides formed,respectively,are:

Give the anomalous properties of lithium.

The function of "Sodium pump" is a biological process operating in each and every cell of all animals. Which of the following biologically important ions is also a constituent of this pump?

Among $KO_2$,$AlO_2^-$,$BaO_2$,and $NO_2^+$,in which species is an unpaired electron present?

Given below are two statements,one is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A$: The alkali metals and their salts impart characteristic colour to reducing flame.
Reason $R$: Alkali metals can be detected using flame tests.
In the light of the above statements,choose the most appropriate answer from the options given below.