Unit vector which is perpendicular to the vector $4\mathrm{î}+3\widehat{\mathrm{j}}$ is _____

The dot product of any two vectors which are perpendicular to each other is 0. The dot product of all the vectors in the options with $4\mathrm{î}+3\widehat{\mathrm{j}}$  is non-zero except for $\widehat{\mathrm{z}}$ . Hence  $\widehat{\mathrm{z}}$ is perpendicular to the given vector.