Boron compounds are rich in variety and have a wide range of uses. Answer the questions with the following information: ⅰ. Boric acid can absorb neutrons and shield nuclear radiation. Its aqueous solu

Boron compounds are rich in variety and have a wide range of uses. Answer the questions with the following information: ⅰ. Boric acid can absorb neutrons and shield nuclear radiation. Its aqueous solution is weak acid. I, (l) boric acid crystal contains H3BO3 molecules, so it is a molecular crystal, so the answer is: molecular crystal;

(2) In the molecule of boric acid [B(OH)3], boron atoms and oxygen atoms form valence bonds, hydrogen atoms and oxygen atoms in hydroxyl groups form valence bonds, and boric acid molecules and boric acid molecules form hydrogen bonds and van der Waals forces.

So, the answer is: b, e, f;

(3) Boron trifluoride (BF3) is hydrolyzed into boric acid and fluoroboric acid (H[BF4]), and the reaction equation is 4BF3+3H2O? 3H[BF4]+H3BO3，

So the answer is: 4BF3+3H2O? 3H[BF4]+h3bo 3；

(4) A. B atoms in boric acid belong to electron-deficient atoms, which can combine with hydroxyl groups dissociated by water in aqueous solution. B(OH)3+H2O=B(OH)4-+H+ is acidic, so it is a monobasic acid, so A is correct;

B. The B atom in boric acid belongs to the electron-deficient atom, so the hydroxyl radical ionized by water can combine in the aqueous solution, which destroys the ionization balance of water, makes the solution acidic and promotes the ionization of water, so B is wrong;

C. The molecular stability is related to the valence bonds of B-O and H-O * *, and the melting point is related to the hydrogen bond, so C is wrong;

D there are only three electrons in the outermost layer of boron atom, which form three pairs of electrons with oxygen atom, so B atom is not 8e stable structure, so D is wrong;

E one H3BO3 molecule corresponds to six hydrogen bonds, and one hydrogen bond corresponds to two H3BO3 molecules, so there are 3 mol hydrogen bonds in the crystal containing 1 molH3BO3 molecule, so e is correct;

So, the answer is: a, e;

Ii. (5) According to the projection, 1 B atom is used by three Mg atoms, so the B atom belonging to one Mg atom is13; 1 Mg atom is used for six b atoms * * *, so the Mg atom used for a b atom is 16, so it can be seen that mg: n (mg): n (b) n =16:13 =1:.

So, the answer is: MgB2；;

Three. (6) The nitrogen atom and the boron atom in the ammonia borane molecule have three single electrons, and their hybrid orbital types are sp3 and sp3, respectively. In the molecule of boric acid [B(OH)3], there are only three electrons in the outermost layer of boron atom, which form three pairs of * * * electrons with oxygen atom. The valence electron pair is 3, the hybridization orbital number is 3, and the hybridization type is sp2.

So the answer is: sp3；; sp2。