In an isosceles triangle , two sides are equal
so we check for option A and C
let us check for each,
option A:
1,1,3
sum of two sides > third side
but here 1+1<3
so this cannot be possible triangle
option C:
{6,6,5}
6+6 =12 >5
6+5=11>6
so it satisfies both the conditions, so option C {6,6,5} is correct