Answer
$BH_3$ is a Lewis acid.
Work Step by Step
- $BH_3$ has, naturally, 3 electrons in its valence shell, and it is making 3 covalent bond with hydrogen. Therefore, this "B" has a total of 6 electrons in its valence shell.
- Since $B$ is from the second row of the periodic table, it has a capacity of holding 8 electrons in its valence shell.
- So, 8-6: there is space for more 2 electrons, which makes $BH_3$ capable of receiving one pair of electrons. - Lewis acid.
