Why `B-X` bond distance in `BX_(3)` is shorter than theoretically expected value ?

Explain why the B - X bond distance in BX_3 is shorter than the theoretically expected value.

The length of the N - Si bond in (SiH_(3))_(3) N is shorter than what is normally expected for an N - Si single bond. This is due to

Though N-F in NF_(3) is a polar bond, the experimental bond length is greater than the theoretically predicted value. Explain.

In BX_(3) B - X distance is shorter than what is expected theoretically because (X = F, CI, Br, I)

In BX_3,B-X distance is shortes than what is expected theoretically because (X = F, Cl Br , I)

Explain the following : (a) Aluminium vessel can be used to store conc HNO_(3) . (b) AlCl_(3) forms a dimer, but BCl_(3) does not. ( c) Al metal is frequency used as a reducing agent for the extraction of metal such as Cr , etc. (d) Al cannot be prepared by the electrolysis of aqueous solution of its salt. ( e) The B-X distance is shorter than what is expected theoretically in BX_(3) molecule (X = F, Cl, Br, I) . (f) Althrough the ionisation potential of B(8.30 eV) is less than gold (9.22 eV) , yet B is a non-metal while gold is a metal.

Why the melting point of manganese is less than the expected value ?