Given that the vectors are coplanar.
That means the determinant is equal to zero.
⇒∣a111b111c∣=0
⇒R1→R1–R2 and R2→R2–R3
⇒∣a−1011−bb−1101−cc∣=0
Expand the determinant along C1.
⇒(a−1)[c(b−1)−(1−c)]+1[(1−b)(1−c)]=0
⇒c(a−1)(b−1)−(a−1)(1−c)+(1−b)(1−c)=0
⇒c(1−a)(1−b)+(1−a)(1−c)+(1−b)(1−c)+(1−a)(1−b)(1−c)=(1−a)(1−b)(1−c)
⇒(1−a)(1−b)+(1−a)(1−c)+(1−b)(1−c)=(1−a)(1−b)(1−c)
⇒1−a1+1−b1+1−c1=1
Hence this is the required option.