Boron hydrides are prepared by the action of dil. HCl on \({Mg_3B_2}\) .
All the B-H bonds in \(B_2H_6\) are not equal. The four terminal B-H bonds are shorter (B-H bond length = 1.19 \(\mathring A\)) than the two bridged B-H-B bonds (bond length - 1.33 \(\mathring A\)).
So, the correct option is (B): All the B-H bonds in $B_2H_6$ are equal.
Method used for separation of mixture of products (B and C) obtained in the following reaction is: 
Let \( \alpha = \dfrac{-1 + i\sqrt{3}}{2} \) and \( \beta = \dfrac{-1 - i\sqrt{3}}{2} \), where \( i = \sqrt{-1} \). If
\[ (7 - 7\alpha + 9\beta)^{20} + (9 + 7\alpha - 7\beta)^{20} + (-7 + 9\alpha + 7\beta)^{20} + (14 + 7\alpha + 7\beta)^{20} = m^{10}, \] then the value of \( m \) is ___________.