15. All the following compounds have rock-salt structure. Which one of them has the smallest lattice enthalpy? (A) LiF (B) NaCl (C) KI (D) MgO (E) SrO

6. Which one of the following functions is the wave function of a sp hybridized orbital of an atom? (A) (1/2)1/2(ψ(s) + ψ(p)) (B) (1/3)1/2ψ(s) - (1/6)1/2ψ(px) + (1/2)1/2ψ(py) (C) (1/3)1/2ψ(s) - (1/6)1/2ψ(px) - (1/2)1/2ψ(py) (D) (1/2)(ψ(s) + ψ(px) + ψ(py) + ψ(pz)) (E) (1/2)(ψ(s) + ψ(px) - ψ(py) - ψ(pz))