molecular forms
... that some solids can reversibly transform between the covalent and molecular forms?
... that some solids can reversibly transform between the <a href="./Bonding_in_solids" id="mwEDk" rel="mw:WikiLink" title="Bonding in solids">covalent</a> and <b id="mwEDo"><a href="./Molecular_solid" id="mwEDs" rel="mw:WikiLink" title="Molecular solid">molecular forms</a></b>?