If your father is currently serving in the Central Industrial Security Force (CISF), you should check the CUET-UG guidelines regarding the definition of "Serving Personnel." Generally, this term applies to candidates themselves rather than their parents. However, some forms consider armed forces or paramilitary personnel’s dependents under specific categories. It is best to refer to the official CUET-UG instructions or contact the exam authorities to confirm whether you need to select "YES" or not based on their criteria.