Which of the following is an alkali metal?

Which of the following statements about the sulphates of alkali metals is correct?

The stability of the following alkali metal chlorides follows the order:

Explain the significance of sodium,potassium,magnesium,and calcium in biological fluids.

Assertion $A$: Alkali metal elements impart characteristic colors to the flame in a flame test.
Reason $R$: They have very low ionization enthalpy.

Discuss the differences in properties observed between lithium and the rest of the alkali metals.