The resultant electric field at point Z is:
\[ E_Z = E_{XZ} + E_{YZ} \]
\[ E_Z = 1.6 \times 10^5 \, \text{N/C} + 8 \times 10^4 \, \text{N/C} \]
\[ E_Z = 2.4 \times 10^5 \, \text{N/C} \]
Thus, the correct answer is:
\[ \boxed{2.4 \times 10^5 \, \text{N/C}} \]