(1) This substance belongs to molecular crystal because of its low melting point. The second periodic elements contained in this substance are C, N and O. For the same periodic element, the first ionization energy of elements increases with the increase of atomic number, but the first ionization energy of IIA and VA elements is greater than that of their adjacent elements, so the order of the first ionization energy of these three elements is n > O > C.

So the answer is: molecular crystals; Nitrogen > oxygen > carbon;

(2) The substance is a molecular crystal, so its melting point is low; N atoms in the molecule of the substance form hydrogen bonds with water molecules to increase its solubility, so the substance is easily soluble in water.

So the answer is: Clopidogrel is a molecular crystal, so its melting point is low; Clopidogrel forms hydrogen bonds with water molecules, so it is easily soluble in water.

(3) During the reaction, each 2- chloro -4- aminopyridine molecule breaks a σ bond and each phenyl isocyanate molecule breaks a π bond. Every 1 mol of clopidogrel requires 1 mol of 2- chloro -4- aminopyridine and 1 mol of phenyl isocyanate, so every 1 mol of clopidogrel,

So the answer is: NA (or 6.02×1023); NA (or 6.02×1023);

(4) Ammonia monohydrate reacts with silver nitrate to generate silver hydroxide precipitate and ammonium nitrate, and silver hydroxide reacts with ammonia monohydrate to generate silver ammonia complex, and the ionic equation dissolved by precipitation is AgOH+2? NH3？ H2O=[Ag(NH3)2]-+OH-+2H2O, so the answer is: AgOH+2? NH3？ H2O=[Ag(NH3)2]-+OH-+2H2O。