Answer : 4. "10 सितंबर"
Explanation :

World Suicide Prevention Day is observed on September 10th each year. This day is dedicated to raising awareness about suicide prevention and promoting worldwide efforts to prevent suicides. It provides an opportunity for individuals, organizations, and governments to come together to work towards reducing the stigma associated with suicide and to promote mental health awareness. Various events and activities are organized globally to support suicide prevention efforts on World Suicide Prevention Day.