Which of the following substances will not get rusted easily?

The correct answer is option 3. Stainless steel.

Stainless steel will not get rusted easily. Stainless steel is an alloy of iron that contains chromium, which forms a thin, protective oxide layer on the surface. This layer inhibits the formation of rust (iron oxide), providing stainless steel with corrosion resistance. A ship submerged in water is likely to be made of materials resistant to rust, such as stainless steel or other corrosion-resistant alloys.  An iron rod exposed to moisture is prone to rusting over time, as moisture and oxygen can react with iron to form iron oxide (rust).

Therefore, the correct answer is Stainless steel.