Step 1: Understand the question.
We must spot the option that is NOT a Fundamental Duty. Fundamental Duties are listed in Article 51A.
Step 2: Check the duties one by one.
Defending the country, valuing our composite culture, and safeguarding public property while shunning violence are all clearly written in Article 51A.
Step 3: Look at the odd one.
Promoting international peace and security is a goal given to the State under Article 51, which is a Directive Principle. It is not a duty placed on individual citizens.
Step 4: Avoid the trap.
The wording sounds noble, so it is easy to think it is a duty. But duties bind citizens, while Article 51 binds the State.
Step 5: Conclude.
The option that is not a Fundamental Duty is the one about international peace and security.
Answer: to promote international peace and security