Answer
The torque on the particle about the origin is $(-50~\hat{k})~N~m$
Work Step by Step
We can find the torque on the particle about the origin as:
$\tau = r\times F$
$\tau = (5\hat{i}+5\hat{j})~m\times (-10~\hat{j})~N$
$\tau = (-50~\hat{k}+0)~N~m$
$\tau = (-50~\hat{k})~N~m$
The torque on the particle about the origin is $(-50~\hat{k})~N~m$.