  We report on the measurement of the scattering properties of ultracold
$^{174}$Yb bosons in a three-dimensional (3D) optical lattice. Site occupancy
in an atomic Mott insulator is resolved with high-precision spectroscopy on an
ultranarrow optical clock transition. Scattering lengths and loss rate
coefficients for $^{174}$Yb atoms in different collisional channels involving
the ground state $^1$S$_0$ and the metastable $^3$P$_0$ are derived. These
studies set important constraints for future experimental studies of
two-electron atoms for quantum-technological applications.
