Answer:
NaHCO3 = No. of atoms are 1 sodium + 1 Hydrogen + 1 carbon + 3 oxygens = 6 atoms per molecule.
In a physical change the appearance or form of the matter changes but the kind of matter in the substance does not. However in a chemical change, the kind of matter changes and at least one new substance with new properties is formed. The distinction between physical and chemical change is not clear cut.
Sand doesn't directly cause weathering because sand is made via weathering. When rocks get weathered they become sand. But maybe when the sand and wind work together they might be able to weather some rocks
