Enter the "Determinant"..??

By Elementary Transposition

$C_4 \rightarrow C_4 - C_3$

$C_3 \rightarrow C_3 -C_2$

$C_2 \rightarrow C_2 -C_1$

Then

$C_4 \rightarrow C_4 -C_3$

$C_3 \rightarrow C_3 -C_2$

Two Columns

$C_3 = C_4$ are equal hence the Determinant is zero. :)