Ammonium formate and silica gel have been found to be efficient reagent combination for an improved and very rapid one-pot synthesis of 2,4,5-trisubstituted and 1,2,4,5-tetrasubstituted imidazoles in excellent yields. Multicomponent condensation in the presence of solid support with operational simplicity, inexpensive reagents, high yield of products, tolerance of sensitive functionalities, use of non-hazardous and non-toxic reagents combination under solvent-less condition makes this synthetic protocol, an attractive one. Moreover, trisubstituted imidazole, 2-(4,5-diphenyl-1H-imidazol- 2-yl)-4-phenylazo-phenol or tetrasubstituted imidazole, 2-(4,5-diphenyl-1- thiazol-2-yl)-1H-imidazol-2-yl)-4-phenylazophenol have been found to be naked eye and colorimetric sensor for anions like F -, Cl -, CH 3COO -, H 2PO 4 - offering very high binding constant with F - ion (K = 1.39 × 10 4 M -1).