Hi Ritu.. :)
Suppose, we have 3 non zero linearly dependent vectors such that:
c1*v1 + c2 *v2 + c3*V3 =0
=> v1 = -(c2/c1)*v2 -(c3/c1)*v3
Now, if you take only one scalar(let it be c1) to be non zero and other two (c2 and c3) be zero
then, v1 = 0 but v1 is a non zero vector which is a contradiction.
Hence, minimum number is 2 and not 1.
:)