2-methylhexane
...that 2-methylhexane and heptane are liquids with the same molecular formula but they have different density, freezing points and boiling points?
...that <b id="mwDa4"><a class="mw-redirect" href="./2-methylhexane" id="mwDa8" rel="mw:WikiLink" title="2-methylhexane">2-methylhexane</a></b> and <a href="./Heptane" id="mwDbA" rel="mw:WikiLink" title="Heptane">heptane</a> are liquids with the same <a class="mw-redirect" href="./Molecular_formula" id="mwDbE" rel="mw:WikiLink" title="Molecular formula">molecular formula</a> but they have different <a href="./Density" id="mwDbI" rel="mw:WikiLink" title="Density">density</a>, <a href="./Melting_point" id="mwDbM" rel="mw:WikiLink" title="Melting point">freezing points</a> and <a href="./Boiling_point" id="mwDbQ" rel="mw:WikiLink" title="Boiling point">boiling points</a>?