(I) All alkali metals react with water, liberating H2 and forming their hydroxides.
2M + 2H2O ---------->2MOH +H2
(II) Alkali metals tarnish in air due to formation of an oxide or hydroxide on their surface.
4Li +O2-------->2Li2 O
2Na +O2--------->Na 2O2
(iii)All alkali metals react with hydrogen to form ionic hydrides.
2M +H2---------->2MH
