Hello,

UPSC has following subjects in the list of optional;

• Agriculture
• Animal Husbandry and Veterinary Science
• Anthropology
• Botany
• Chemistry
• Civil Engineering
• Commerce & Accountancy
• Economics
• Electrical Engineering
• Geography
• Geology
• History
• Law
• Management
• Mathematics
• Mechanical Engineering
• Medical Science
• Philosophy
• Physics
• Political Science & International Relations
• Psychology
• Public Administration
• Sociology
• Statistics
• Zoology

there are also following literature subjects such as

• Assamese
• Bengali
• Bodo
• Dogri
• Gujarati
• Hindi
• Kannada
• Kashmiri
• Konkani
• Maithili
• Malayalam
• Manipuri
• Marathi
• Nepali
• Oriya
• Punjabi
• Sanskrit
• Santhali
• Sindhi
• Tamil
• Telugu
• Urdu
• English

Nursing as a subject isn't included in the list of optional, the syllabus of any optional subject is based on graduation level, hence your interest matters a lot here, also availability of study materials, the level of the syllabus as in how vast it is etc, so you can consider these factors when selecting your optional subject, there is no such thing as choosing one will make you score more, it's always about how well you have written the paper, your knowledge and having a good hold over the subject matters, so consider these parameter prior to deciding upon any subject as optional in upsc.