Why are metallic and ionic substances harder to melt than covalent substances

Why does a plastic bottle that is sealed at a high altitude change it’s shape when taken to lower altitude

Increasing the substrate concentration in an enzymatic reaction could overcome which of the following? a) the need for a coenzymeb) allosteric inhibitionc) competitive inhibitiond) insufficient cofactors

The equation picture below shows which type of nuclear reaction u 235 + n x e 134 + sr 100 + 2n