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1. Answer in brief: (2×10=20)

i) The BF3molecule has a planar triangular structure with B at the centre. List the

symmetries of the BF3 molecule.

ii) In an orthorhombic crystal a lattice plane makes intercepts of 2a, 3b and 4c on the

three axes. Write down the Miller indices for this plane.

iii) Explain what type of bonding is expected to be observed in KCl.

iv) The energy of the lowest allowed level for an electron in a 1-D box is 10.0 eV.

Can the electron ever have an energy of 200 eV? Justify.

v) Show that the group velocity is zero at edge of the first Briclouin zone for a linear

monoatomic chain.