Which of the following properties is not true for an alkali metal?

The commercial production of sodium carbonate is done by

Magnesium burns in air to give

The solution of sodium metal in liquid ammonia is strongly reducing due to the presence of which of the following in the solution?

Which element of group-$1$ has the highest hydration enthalpy? Why?

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.