H2SO4 is an acid
the chemical equation showing how H2SO4 is an acid according to the Arrhenius definition is as below
H2SO4 dissociate to give 2H^+ and SO4^2-
that is H2SO4 = 2H^+ + SO4^2-
According to Arrhenius an acid dissociate to give H^+ ions H2SO4 is an acid since it dissociate to give two hydrogen ions
A matter in the solid phase has a fixed shape and volume.