(c)
If $\overrightarrow{\mathbf{a}}\mathbf{,}\overrightarrow{\mathbf{b}}$ are two non-zero non-collinear vectors and $x,y$ are two scalars such that $x\overrightarrow{\mathbf{a}} + y\overrightarrow{\mathbf{b}} = 0,\ then\ x = 0,\ y = 0$.
Because otherwise one will be a scalar multiple of the other and hence collinear, which is a contradiction