The vectors $\overrightarrow{2i}+\overrightarrow{3j}+\overrightarrow{4k}$ and $\overrightarrow{ai}+\overrightarrow{bj}+\overrightarrow{ck}$ are perpendicular when

Question

$$\begin{array} {1 1}(1)a=2, b=3 ,c=-4 &(2)a=4 ,b= 4 , c=5\\(3)a=4 ,b = 4 ,c=-5 &(4)a=-2 ,b=3 ,c=4 \end{array}$$