$$(a)$$ Find the angle $$\theta $$ between adjacent nearest-neighbor bonds in the silicon lattice. Recall that each silicon atom is bonded to four of its nearest neighbors.The four neighbors form a regular tetrahedron—a pyramid whose sides and base are equilateral triangles. $$(b)$$ Find the bond length, given that the atoms at the corners of the tetrahedron are $$388$$ pm apart.

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