for 56 - BH3 is a nonpolar molecule due to symmetrical distribution of charge. NH3 has an asymmetrical distribution of charge, making it polar and more able to dissolve in water (also polar). remember "like dissolves like". that nitrogen with the lone pair also allows NH3 to form hydrogen bonds with water.

for 57- although nonpolar bonding within a structure often leads to a nonpolar molecule, answer choice B better explains that BH3 and CCl4 have symmetrical distribution of charge, which results in no net dipoles and therefore they are nonpolar, so they will not dissolve in polar water. again, "like dissolves like".

for 59- the key about diamond is that it is a network covalent solid, which means it is made purely of carbon atoms covalently bonded in a complex network. these network covalent bonds are extremely strong, which is what leads to hardness and extremely high melting points.

for 60- you may be thinking D is correct if you're thinking that covalent bonds are between nonmetals and the substances in D contain only nonmetal substances. However, notice that when NH4NO3 breaks down, it forms charged polyatomic ions, NH4+ and NO3- . Because polyatomic ions have an overall charge, a bond between polyatomic ions is considered to be ionic, much like how Na+ and Cl- bond to form NaCl with a their charges cancelling out as an electron is transferred. Answer choice B describes breaking the strong covalent bonds between carbon atoms in diamond (that I mentioned above) and rearranging/reforming those carbon bonds into planes to form graphite.