Answer:
The order is
Quartz > Calcium > Ammonia > Chlorine
Step-by-step explanation:
Among given compounds
Quartz is a covalent compound with extensive bondings and thus it will have highest melting point
Calcium is a metal so it will have strong metallic bonds thus will have high melting point, however less than quartz.
ammonia is a polar molecule with weak hydrogen bond as intermolecular interactions thus will have higher melting point than chlorine
chlorine is a non polar molecule with weak intermolecular london dispersion forces.