\(BC{l_3} + \frac{3}{2}{H_2} \to B + 3HCl\);
\(B = \frac{{21.6}}{{10.8}} = 2\)
\(B \equiv \frac{3}{2}{H_2}\)
\(1\) \(mole\) \( \equiv \frac{3}{2}\) \(mole\) ; \(2\) \(mole\) \(-3\) \(mole\)
\(V = 3 \times 22.4 = 67.2\,L\)
(પરમાણ્વીય દળ, $Ba=137\,amu, Cl=35.5\,amu$)