The process which is not helpful in the prevention of rusting of iron is annealing.

Explanation:
Rusting is a common chemical process that occurs when iron or steel comes into contact with oxygen and moisture. It leads to the formation of iron oxide or rust on the surface of the metal, which weakens it over time. Various methods are employed to prevent the rusting of iron, but not all processes are equally effective.

Annealing:
Annealing is a heat treatment process used to soften metal, improve its ductility, and reduce internal stresses. It involves heating the metal to a specific temperature and then cooling it slowly. Annealing does not provide any protection against rusting because it does not involve the application of any protective coating or barrier. The process only alters the internal structure of the metal, making it more malleable and less prone to cracking or breaking. However, the surface of the metal remains exposed to oxygen and moisture, leaving it susceptible to rusting.

Other processes:
On the other hand, the other options mentioned - applying grease, galvanizing, and painting - are effective methods for preventing rusting. Let's briefly discuss each of them:

- Applying Grease: Grease acts as a physical barrier between the metal surface and the surrounding environment, preventing the contact of oxygen and moisture with the iron. It creates a protective layer that inhibits the formation of rust.

- Galvanizing: Galvanizing involves coating the iron or steel with a layer of zinc, either by hot-dip galvanizing or electroplating. Zinc acts as a sacrificial anode, corroding before the iron does. This sacrificial protection prevents the iron or steel from rusting.

- Painting: Painting the surface of iron or steel with a layer of paint creates a protective barrier that prevents direct contact between the metal and the environment. The paint acts as a shield, blocking oxygen and moisture from coming into contact with the iron surface.

Conclusion:
While annealing is a useful process for improving the properties of metal, it does not provide any protection against rusting. To prevent rusting, it is necessary to employ methods such as applying grease, galvanizing, or painting, which create barriers between the iron surface and the surrounding environment.