Final answer:
Natural active immunity is the type of immunity that develops when a strong antigen invades the body, stimulating the body's immune response and leading to the production of antibodies and memory cells for long-lasting protection.
Step-by-step explanation:
The type of immunity that will develop when a strong antigen invades the body is natural active immunity. Natural active immunity is acquired when the body's own immune system is activated due to exposure to the antigen, such as during an infection. The immune response results in the production of antibodies and memory cells, providing long-lasting protection against future infections by the same antigen.