Nitrous oxide-acetylene flames are extensively used as atom reservoirs and as excitation sources for spectroscopic determination of elements. A 'carbon-rich nitrous oxide-acetylene flame has a relatively high temperature and a reducing nature'--this combination of desirable properties in a flame makes it form free atoms in electronic ground state even from those elements which exist almost totally as monoxides in fuel-deficient or cooler flames. Five elements, viz. Ti, Zr, Hf, Nb and Ta were selected on the basis of stability of their monoxides (i.e., formation of few atoms in fuel-deficient and cooler flames). By measuring the spatial distributions (profiles) of the flame temperature and the population density of atoms in the electronic ground state, and the intensity of monoxide emission and efficiency of atom formation (e$ value), it has been possible to assess the importance of different factors in producing free atoms, and also, to propose a model for the formation of free atoms of these elements. The dissociation energies of different monoxides have been calculated from the 3-factors. No correlation between the 3-factors and the dissociation energies has been found. However, the 3-factors have been found to depend on the compound/solvent system and the flame characteristics, viz., the fuel and the oxidant (which together determine the burning velocity, and hence, the residence time of the solute particle in the flame), the chemical composition, the oxidizing and reducing nature and the temperature of the flame.