X and Y react according to the equation ${\text{2X}} + {\text{Y}} \to {\text{Z}}$. The reaction can be described by the following mechanism:

${\text{X}} + {\text{X}} \to {{\text{X}}_2}$     slow

${{\text{X}}_2} + {\text{Y}} \to {\text{Z}}$     fast

What is the order of the reaction with respect to X and Y?

C