For which of these vectors is the projection on the $y$-axis zero?

(i) $2\hat{j}$
(ii) $-5\hat{k}$
(iii) $\hat{i} - 4\hat{k}$

only (ii) and (iii)

The correct answer is Option (4) → only (ii) and (iii) ##

If the coefficient of $\hat{j}$ in the given vector is zero, then the vector lies in the $XZ$ plane and therefore, the projection of the vector on $y$-axis is zero.