Transgenic animals are not used for:

The correct answer is Option (4) → Development of biological weapons

A transgenic animal is an animal whose DNA has been changed so that it carries and expresses an extra gene of another species. Over 95 per cent of the existing transgenic animals are mice. They are made for these purposes: to study normal physiology and development, to study diseases, to obtain biological products, to test the safety of vaccines, and to test the safety of chemicals.

(1) Understanding the normal physiology and development — A use of transgenic animals. Genes are changed to see how they control the working and the growth of the body.

(2) Study of particular genetic disease — A use of transgenic animals. Animals serve as models of human diseases such as cancer and cystic fibrosis.

(3) Obtaining biological products — A use of transgenic animals. They can make useful products such as human protein for treating emphysema.

(4) Development of biological weapons — Not a use of transgenic animals. It is not among the purposes for which they are made.

NCERT Extract:
Transgenic Animals – “… (i) Normal physiology and development: Transgenic animals can be specifically designed to allow the study of how genes are regulated, and how they affect the normal functions of the body and its development, e.g., study of complex factors involved in growth such as insulin-like growth factor. By introducing genes from other species that alter the formation of this factor and studying the biological effects that result, information is obtained about the biological role of the factor in the body.”
Transgenic Animals – “… (ii) Study of disease: Many transgenic animals are designed to increase our understanding of how genes contribute to the development of disease.”
Transgenic Animals – “… (iii) Biological products: Medicines required to treat certain human diseases can contain biological products, but such products are often expensive to make.”