ionic dropdown selection

   <ion-card>

    <ion-item>

      <ion-label>Select Subject</ion-label>

      <ion-select  [(ngModel)]="itemId" (ionChange)="optionsFn();" >

      <ion-select-option  *ngFor ="let c of Categories;let id = index"

 [value]="[id]">{{c.CatagoryName}}</ion-select-option>

      </ion-select>

    </ion-item>

  </ion-card>

  optionsFn(){debugger

this.subcategory=this.Categories[this.itemId].children

console.log(this.subcategory)

  }