Question

Why alkali metals are very reactive?

Answer 1

these metals have 1 electron in outermost shells sothey loose electron readily and form ionic bond

Answer 2

Alkali metals are the metals having most metallic character because they are the largest in size along the period i.e. we go left to right.
Due to their large size they have low ionization enthalpy and losse the electron very easily and react with any electron aceeptor .
so they are found mostly in compounds i.e. they are very reactive.☺