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

Iknow the answer is a but i don't know why

2. you__turn left on a red light if you are in the left-most lane of a one-way street, you're turning into the left-most lane of a one-way street, and no nearby sign prohibits the turn.

Using the thermodynamic information in the aleks data tab, calculate the standard reaction free energy of the following chemical reaction: →+p4o10s6h2ol4h3po4s round your answer to zero decimal places.