Answer
See work below for details.
Work Step by Step
Compounds composed of boron and hydrogen, called boranes, form many unique cluster, cagelike, and netlike structures.
The $closo-boranes$ have the formula $B_{n}H_{n}^{2-}$ and form fully closed polyhedrons with triangular sides. A boron atom, with an attached hydrogen atom, occupies each of the vertices in the polyhedrons.
If the borane polyhedron is missing one or more boron atoms, extra hydrogen atoms attach to the structure to make the borane neutral.
We can classify these neutral boranes on the basis of their different chemical formulas. The $nido-boranes$, named from the Latin word for nest, have the formula $B_{n}H_{n}^{+4}$. They consist of a cage of boron atoms missing one corner.
The $arachno -boranes$, named from the Greek word for spiderweb , have the formula $B_{n}H_{n}^{+6}$. They consist of a cage of boron atoms that is missing two or three corners.
